Calendar sync has its own vocabulary, and most of it is borrowed from standards and APIs that were never meant to be read by the people who depend on them. This glossary defines the terms in plain language, in the order someone setting up a sync tends to meet them. Each entry stands on its own, so you can link straight to the one you need.
What is calendar sync?
Calendar sync keeps two or more calendars showing the same events without you copying anything by hand. When you add, change, or delete an event in one calendar, a sync tool detects the change and makes the matching change in the others. Hetk does this between Google Calendar, Microsoft Outlook, and Apple iCloud.
What is one-way sync?
One-way sync copies events from a source calendar into a target calendar, and only in that direction. Edits made in the target do not flow back to the source. It is the right choice when one calendar should mirror another but never change it — for example, copying a client’s calendar onto your own so you can see their bookings.
What is bi-directional sync?
Bi-directional (two-way) sync flows changes in both directions. Add an event in either calendar and it appears in the other; edit or delete it on one side and the other follows. This is what most people mean by “keeping my calendars in sync.” The trade-off is that you need a rule for conflicts, which is why sync tools resolve simultaneous edits by keeping the most recent change.
What is a sync pair?
A sync pair is one relationship between two specific calendars, pointed in a chosen direction with chosen privacy settings. Syncing your work Google calendar with your personal iCloud calendar is one pair. Hetk’s plans are priced by the number of sync pairs, not the number of connected calendars — calendars are unlimited on both plans.
What is CalDAV?
CalDAV is the open standard for reading and writing calendar data over the web, built on top of WebDAV. Apple iCloud, Fastmail, and many self-hosted calendar servers speak it. Hetk connects to iCloud over CalDAV because iCloud has no separate calendar API.
What is an app-specific password?
An app-specific password is a single-purpose password you generate for one application, so you never hand over your main account password. Apple requires one for any third-party tool that connects to iCloud calendars over CalDAV. You create it at appleid.apple.com, and you can revoke that one password later without touching your Apple ID or anything else connected to it.
What is OAuth?
OAuth is the standard that lets you grant an app limited access to your account without giving it your password. When you connect Google or Microsoft to Hetk, you sign in with the provider and approve a specific set of permissions; the provider hands Hetk a token, not your credentials. You can revoke that token from your Google or Microsoft account at any time.
What is an OAuth scope?
A scope is one specific permission inside an OAuth grant. Rather than “access to your account,” scopes are narrow — for example, read and write calendar events but nothing else. Hetk requests only the calendar scopes it needs and no access to mail, files, or contacts.
What is admin consent?
In Microsoft 365 and Google Workspace, an administrator can require that third-party apps be approved at the organisation level before any employee can connect them. If you see “Need admin approval” when connecting Outlook, that is admin consent: your IT admin approves Hetk once, and then people in the organisation can connect.
What is a webhook?
A webhook is a message a calendar provider sends the moment something changes, so a sync tool can react immediately instead of asking “anything new?” on a timer. Google and Microsoft support webhooks, which is why changes from those providers sync within seconds.
What is polling?
Polling is the fallback for providers that do not send webhooks: the sync tool checks for changes on a schedule. Apple iCloud has no push notifications, so Hetk polls each connected iCloud calendar every few minutes. That makes iCloud-originated changes land in minutes rather than seconds.
What is an ICS file?
ICS (iCalendar) is the standard file format for calendar data. You can export events as a .ics file and import them elsewhere, or subscribe to an ICS URL for a read-only copy of someone else’s calendar. ICS subscriptions are not real sync — they refresh slowly, on the receiving calendar’s schedule, and changes never flow back.
What is free/busy?
Free/busy is the availability layer of a calendar: whether a block of time is taken, without revealing what it is. Sync tools can copy an event as a plain “Busy” block so a shared calendar shows you are unavailable while the title, location, and attendees stay private.
What is an all-day event?
An all-day event has a date but no specific start and end time. Syncing them correctly across providers is fiddly because each provider stores time zones differently, so a tool has to preserve the all-day flag rather than turning the event into a 24-hour block.
What is a recurring event?
A recurring event repeats on a rule — every weekday, the first Monday of the month, and so on — stored as a single series rather than hundreds of copies. The rule is called an RRULE. Sync has to handle both the whole series and any single occurrence you change on its own.
What is the sync window?
The sync window is the span of time a tool actually keeps in sync, rather than your entire calendar history. Hetk syncs events from 3 months in the past to 12 months in the future, which covers the events that matter without copying years of stale history.