Calendar Glossary
28 terms every calendar user should know
Last updated: April 2026 | Covers Google Calendar, Apple Calendar, and Outlook
Your calendar app does a lot more than you think, and it uses a lot of words you have probably never had a reason to look up. That is fine. Most people open their calendar, check what is happening today, and move on.
But at some point, something weird happens. A calendar you deleted comes back. Events show up that you cannot edit. Your kid's school schedule stops updating and you miss a half day. When that moment arrives, a little vocabulary goes a long way.
This glossary covers 28 terms you might run into when subscribing to calendars, syncing across devices, or trying to figure out why something is not working. Each one is written for a normal person, not a developer. If you are looking for platform-specific help, see our guides for Google Calendar, Apple Calendar, and Outlook.
Subscriptions and Feeds
Calendar subscription
A calendar subscription is a live connection between a calendar source and your calendar app. You set it up once, and from that point on, your app automatically receives any new events, changes, or cancellations from the source. You do not have to do anything after the initial setup.
The events that arrive through a subscription are read-only, which means you cannot edit them. That might feel like a limitation, but it is actually the point. The source controls the data, so you are always seeing the most current version. If your kid's school changes a PA day, the update just shows up on your calendar without you having to do anything.
Here is something most people do not realize: subscribing and importing are completely different things, and mixing them up is the number one reason people end up with calendars that seem broken. More on that in the next two entries.
Calendar import
A calendar import is a one-time copy of events into your calendar app. At the moment you import, everything looks perfect. But from that point forward, the events are frozen. If the source changes a date, adds a new event, or cancels something, your imported copy just sits there showing the old information.
Importing makes sense for things that will genuinely never change, like a record of past events you want to keep. For anything that could be updated in the future, such as a school calendar, a sports schedule, or a community events calendar, subscribing is almost always what you want instead.
Import vs. subscribe
This is the single most important distinction in this entire glossary, and it trips up more people than any other calendar concept.
Importing creates a static copy. Subscribing creates a live connection. Same calendar data, completely different behavior.
Here is a concrete example. You find your school district's calendar online as an .ics file. If you import it in September, your calendar shows every event as of that moment. Looks great. But when the school adds a snow day in January, your calendar has no idea. It is still showing the September version. If you had subscribed to that same .ics file instead, the snow day would appear automatically.
The tricky part is that most people do not know they chose one over the other. Many calendar apps make the choice based on how you open the file. Clicking a webcal:// link usually subscribes. Downloading a .ics file and opening it from your downloads folder usually imports. If your calendar feels stuck on old data, this is the first thing to check.
.ics file
An .ics file is the universal file format for calendar data. Think of it like a PDF for calendars. It does not matter whether the calendar was created in Google, Apple, Outlook, or something else entirely. If it is an .ics file, any calendar app can read it.
The name stands for iCalendar Specification, which sounds very technical, but all you really need to know is that .ics is the file extension you will see when someone shares a calendar with you.
The same .ics file can be used two different ways. You can download it and import it (a frozen snapshot), or you can subscribe to its URL so your app checks back for updates on a regular schedule. The file is the same either way. The difference is entirely in what your app does with it.
ICS format (iCalendar)
The ICS format is the technical standard, defined in a document called RFC 5545, that dictates how calendar events are structured inside an .ics file. It spells out exactly how a title, start time, end time, location, and description should be written so that every calendar app in the world can read them the same way.
You will never need to open or edit an ICS file yourself. But the format is worth knowing about because it is the reason calendars from completely different platforms can talk to each other. A school district publishing events from Google Calendar, a sports league using some custom system, and you subscribing from your iPhone are all connected by this one shared format.
Calendar feed
A calendar feed is simply a URL that serves calendar data. Your calendar app visits this URL on a schedule, and each time it does, it picks up the latest events. You might hear people say calendar feed, subscription URL, or ICS feed. They all mean the same thing: a web address your app keeps checking for updates.
When someone says "subscribe to our calendar feed," they are asking you to give your calendar app their URL so it can stay in sync automatically. That is it. No account to create, no app to install. Just a URL and a subscription.
webcal://
webcal:// is a special URL prefix that tells your device to open a link in your calendar app instead of your web browser. If you click a regular https:// link to an .ics file, your browser might just download the file. If you click a webcal:// link to the exact same file, your phone or computer opens your calendar app and offers to subscribe.
The prefix was originally created by Apple back in 2002 for their iCal application, but it works on most platforms now. Google Calendar, Apple Calendar, and Outlook all understand webcal:// links.
Here is a useful thing to know: webcal:// and https:// links often point to the exact same calendar data. The only difference is what happens when you click. If a webcal:// link is not working for some reason, try replacing webcal:// with https:// and pasting the URL into your calendar app's "subscribe by URL" option. You will get the same calendar.
Refresh interval
The refresh interval is how often your calendar app checks a subscribed feed for new or updated data. And this is one of the most misunderstood things about calendar subscriptions.
When a school publishes a schedule change, it does not magically appear on your phone. Your app has to go out and check the feed URL to discover the change. How often it does that depends on which app you use, and the differences are significant.
Google Calendar checks roughly every 12 to 24 hours. You cannot change this. There is no setting for it, no way to force a refresh, and no workaround. It is just how Google Calendar works. Apple Calendar, on the other hand, lets you choose your own refresh interval, anywhere from every 5 minutes to once a week. You can find this setting when you set up the subscription on a Mac. Outlook falls somewhere in the middle, refreshing every 3 to 24 hours with no user control and inconsistent timing.
If your subscribed calendar feels out of date, it probably is, but only temporarily. The source may have already published the change. Your app just has not checked yet. This is a platform limitation, not a problem with the feed.
Apps, Accounts, and Sync
Calendar app
A calendar app is the application you use to view and manage your schedule. Apple Calendar, Google Calendar, and Outlook are all calendar apps. The built-in calendar on your phone is a calendar app.
Here is the key insight that changes how you think about your calendar: your app is just a viewer. It does not actually store your events. It displays events from one or more calendar accounts, which live somewhere else entirely (more on that in the next entry).
Think of it like an email app. Your Gmail app can show you messages from Gmail, your work email, and your personal Outlook account, all in one inbox. Your calendar app does the same thing with calendars. One app, multiple sources, all displayed together.
Calendar account
A calendar account is the service that actually stores your calendar data. iCloud, Google, and Microsoft Exchange are calendar accounts. Your calendars live in your account, not in your app.
This is a genuinely important distinction, and here is why: if your phone breaks, gets lost, or you switch to a new one, your events are not gone. They were never stored on the phone. They live in your account in the cloud. Sign into the same account on your new phone and everything comes back.
When something goes wrong with your calendar, the first question to ask is whether the problem is with your app or your account. If events are missing on your phone but visible when you log into the web version of your calendar, the problem is with your app or its sync settings. If events are missing everywhere, the problem is with the account.
Calendar app vs. calendar account
This is the most commonly confused concept in calendar management. It causes more frustration than any other misunderstanding, because the fix for an app problem is completely different from the fix for an account problem.
Your app is what you see on your screen. Your account is where your data lives. They are separate things.
Here is an example that makes it concrete. You might use Apple Calendar (the app) on your iPhone, and inside it you see events from three different places: your personal iCloud calendar, your work Exchange calendar, and a Google Calendar you share with your spouse. That is one app showing calendars from three accounts.
When you hear someone say "my calendar is not working," the most useful first question is: which calendar? Which account? Is it just one account that is broken, or all of them? The answer usually points straight to the fix.
Subscribed calendar
A subscribed calendar is a calendar in your app whose events come from an external feed. The events show up on your schedule just like your own events, but with one important difference: you cannot edit them.
The read-only nature makes sense when you think about it. The events are controlled by whoever publishes the feed. Your kid's school sets the calendar. The sports league sets the game times. You are viewing their data, not your own. If you could edit it, you would just be editing your local copy, which would then get overwritten the next time your app refreshes from the feed.
If you see events on your calendar that you cannot tap into and change, they are almost certainly from a subscription or a shared calendar with view-only permissions.
Shared calendar
A shared calendar is a calendar that another person has given you permission to see, and sometimes to edit. Your coworker sharing their work schedule, your partner sharing a family calendar, or a team calendar at work are all examples of shared calendars.
The key difference from a subscribed calendar is that shared calendars can be two-way. Depending on the permission level the owner gives you, you might be able to add events, change times, or delete things. With a subscription, you can only view.
Shared calendars sync in real time through the calendar service (Google, Exchange, iCloud), which is faster and more reliable than the periodic refresh that subscriptions use. When your coworker adds a meeting to a shared calendar, you usually see it within minutes, not hours.
Published calendar
A published calendar is a calendar that someone has made available via a public URL so that anyone with the link can subscribe to it. Schools, sports leagues, houses of worship, and community organizations publish calendars this way.
One thing worth knowing: the URL is the access key. Anyone who has it can see every event on the calendar. If the calendar contains private information, the URL should be treated like a password. It should not be posted on a public webpage without understanding that anyone can subscribe.
Platforms and Protocols
CalDAV
CalDAV is a behind-the-scenes protocol that allows two-way calendar sync between a server and your calendar app. When you add your iCloud account to a calendar app and your events appear and stay in sync, CalDAV is doing the work.
What makes CalDAV different from a regular calendar subscription? Subscriptions are one-way: the feed sends events to your app, and that is it. CalDAV is two-way: your app can read events from the server, and it can also create, edit, and delete events on the server. It is a full conversation, not a broadcast.
Most people use CalDAV every day without knowing it exists. If you have an iCloud account connected to any calendar app, CalDAV is running in the background.
Exchange / Microsoft 365
Exchange is Microsoft's email and calendar platform, and it is the backbone of calendar systems at most large companies. If you have a work email that ends in your company's domain and it connects through Outlook, you are almost certainly on Exchange or its cloud version, Microsoft 365.
Here is why Exchange matters for your personal calendar life: it is the most common source of ghost calendars after you leave a job. When your employer deactivates your corporate account, the calendar data can linger on your personal devices for weeks or months. Old meetings, team events, and reminders just sit there, often in a read-only state that you cannot easily delete. The fix is to find the Exchange account in your phone's settings and remove it completely.
Google account (calendar context)
Your Google account stores your Google Calendar data. This feels obvious, but the implications are worth spelling out: when you add your Google account to Apple Calendar or Outlook, all your Google calendars show up inside those apps. The events still live in Google. You are just viewing them through a different app.
This is useful because it means you can use whichever calendar app you prefer without losing access to your Google Calendar data. Many iPhone users keep their Google account connected to Apple Calendar specifically so they can see Google Calendar events alongside their iCloud events in one place.
iCloud
iCloud is Apple's cloud service, and among other things, it stores your Apple Calendar data and syncs it across all your Apple devices. When you create an event on your Mac, it shows up on your iPhone and iPad automatically. iCloud is doing that.
There is a practical tip here that catches a lot of people: when you subscribe to a calendar on a Mac, you get to choose where to store the subscription. If you choose iCloud, the subscription appears on all your Apple devices. If you choose On My Mac, it stays only on that computer. This is the number one reason people subscribe to a calendar on their Mac and then wonder why it does not show up on their phone.
Inside the .ics File
You will probably never open an .ics file and look at its contents. But the terms below describe the building blocks inside it, and knowing what they are helps explain some odd calendar behaviors that would otherwise seem like bugs.
VCALENDAR
VCALENDAR is the outer container in every .ics file. Think of it as the envelope. The file starts with BEGIN:VCALENDAR and ends with END:VCALENDAR, and everything else - events, time zones, alarms - lives inside it.
VEVENT
A VEVENT is a single event inside an .ics file. It holds the event's title (called SUMMARY in the file), its start time, end time, description, location, and any other details. A school calendar feed with 200 events throughout the year contains 200 VEVENTs, all wrapped inside one VCALENDAR.
VTIMEZONE
A VTIMEZONE is a time zone definition embedded in an .ics file. It tells your calendar app how to correctly display event times for your local time zone. Without it, an event created by someone in Eastern Time could show up at the wrong time for you if you are in Pacific Time.
Well-built calendar feeds always include VTIMEZONE entries. If you subscribe to a feed and all the events seem to be off by a few hours, the feed is probably missing proper time zone data.
VALARM
A VALARM is an alert or reminder attached to an event inside an .ics file. It tells your calendar app when to notify you before the event starts.
Here is something useful to know: many calendar apps silently ignore VALARM entries from subscribed feeds and use their own notification settings instead. If you subscribe to a calendar and never get reminders for its events, this is probably why. Check your app's per-calendar notification settings rather than assuming the feed is broken.
UID
A UID is a unique identifier assigned to each event in an .ics file. It is the mechanism your calendar app uses to tell the difference between a brand-new event and an update to an event it already has.
When a school changes a game time from 3:00 to 4:00, the feed publisher updates the event but keeps the same UID. Your app sees the UID, matches it to the game already on your calendar, and updates the time instead of creating a second copy of the same game.
This also explains one of the most common duplicate event problems. If you subscribe to the same calendar through two different methods (say, one subscription through Google Calendar and another through Apple Calendar), your apps cannot match UIDs across accounts. You end up with two copies of every event.
Common Calendar Problems
Ghost calendar
A ghost calendar is a calendar that shows up in your app but cannot be found when you go looking for it in settings. There is no option to delete it. There is no account it belongs to. It just sits there, sometimes showing old events, sometimes empty, always annoying.
Ghost calendars almost always come from one of three situations: you left a job and the old Exchange account was removed but not cleanly (this is the most common one); you upgraded your operating system and old calendar data from a previous sync method got stranded; or you removed and re-added an iCloud account and something did not reconnect properly.
The fix depends on the source, but the first step is always the same: go to your phone or computer's account settings (not the calendar app's settings) and look for accounts you no longer recognize or use. Removing the orphaned account usually takes the ghost calendar with it.
Calendar spam
Calendar spam is exactly what it sounds like: unwanted events that appear on your calendar without your permission. They typically have alarming titles like "Your phone has been compromised" or "Click here to claim your prize" and are designed to get you to tap a malicious link.
Calendar spam usually gets onto your device one of two ways. Either you accidentally tapped a web popup that subscribed you to a spam calendar without you realizing it, or a spammer sent calendar invitations to your email address and your app automatically added them.
The most important thing: do not tap any links in the events, and do not tap Decline on the invitation (declining confirms to the spammer that your address is active). Instead, find the spam subscription in your calendar settings and delete the entire calendar. On iPhone, go to Settings, then Calendar, then Accounts, then Subscribed Calendars, and delete anything you do not recognize. Apple also added a Report Junk feature specifically for this.
Read-only events
Read-only events are events on your calendar that you can see but cannot change or delete. You tap on them and there is no edit option, or the fields are grayed out.
This happens for two reasons. Either the events come from a subscribed calendar (which is always read-only by design), or they come from a shared calendar where you only have view permission. In both cases, the person or organization that controls the source is the only one who can make changes.
There is a specific frustration worth mentioning: after certain macOS and iOS updates, Exchange calendar events displayed in Apple Calendar sometimes lose their edit permissions even when you should have them. If events you used to be able to edit are suddenly read-only after an update, this is likely what happened. Re-adding the Exchange account usually fixes it.
Primary calendar
Your primary calendar is the default calendar attached to your main account. In Google Calendar, it is the one named after your email address. In Apple Calendar, it is the default calendar in your iCloud or local account. You cannot delete it.
Here is a practical implication that trips people up: when you create a new event, it goes into your primary calendar unless you specifically pick a different one. If you have multiple calendars (personal, work, family) and all your events keep landing in the same one, check which calendar is set as your default.
In Outlook, there is a known bug where subscribed calendars sometimes merge into the primary calendar instead of appearing as their own separate calendar in the sidebar. This makes the subscription's events look like they are your own events, and removing the subscription becomes much harder because there is no separate calendar to delete. This is documented in multiple Microsoft support threads and has not been fixed.
Other calendars
"Other calendars" is a section in Google Calendar's sidebar that contains calendars you have subscribed to, calendars you imported from URLs, and holiday calendars you have added. There is also a separate section called "Other people's calendars" for calendars shared with you by specific people.
Apple Calendar has a similar section called "Other" in its calendar list, which holds system-generated calendars like Siri Suggestions, subscribed feeds, and sometimes calendars from accounts that are not fully syncing.
If you subscribe to a calendar and cannot find it in your list, check these sections. Subscriptions often land here instead of under your main account, which confuses people who are looking in the wrong place.
Changelog
April 2026: Initial publication. 28 terms across five sections.