Your calendars (Google Calendar, CalDAV, iCal address). Connecting a calendar is optional. If you connect one, we use it in two ways only.
1. We read the start, end and title of your events on the days of a meeting you take part in, and of the coming weeks if you use the availability page or look at My availability (four weeks, unless you set another number in your profile, at most twelve), and leave these times out of the availability you marked. We read them when you save availability, set up or open a meeting, open My availability, or when somebody opens your availability page. Events that last whole days, that are marked as free or that you declined are ignored. The times and titles are stored on our own server with your availability for that meeting and are removed with it. The titles are only shown to you. Other participants, and visitors of your availability page, see only when you are available or busy. With Google Calendar we also read the list of your calendars, so that you can choose which of them count.
2. Once a meeting has a confirmed time, we add it to your calendar (Google Calendar and CalDAV). If you are its host (or the one a time was booked with), the entry names the other participants whose address you were given as guests, so that your calendar server invites them in your name. We change or remove that entry when the meeting changes. We do not change or remove any other events by ourselves. If you remove an entry of your calendar yourself with the x on it in the grid, we take it out of that calendar and keep it in encrypted form for a day, so that you can put it back.
If you switch on the free/busy feed in your profile, whoever has its address gets the times you are busy from all your calendars and meetings together, as "busy" without titles; your calendars are then also read when that address is fetched. If you join the availability page of a group (with its invite link, after being told this), the page shows when you are free in the coming weeks, computed from your usual week (the one of My availability, or one you mark on the page for that group only, which is kept with the page and removed when you leave it), your calendars and your meetings scheduled here: the times only, never what you have then. Who sees that is set for the page and said before you join: all its members with your name, or only its host while the others see how many members are free at a time, or nobody but such numbers. Members (on an anonymous page only its host) can schedule a meeting with you at once, which is then among your scheduled meetings. The e-mail address of your profile, if you gave one and are not anonymous, is kept with the page when you join: whoever schedules such a meeting can invite you at it and sees it then (not on a page where nobody sees who is who). Nobody who is not a member gets any of it, the page is not listed anywhere, and you can leave it at any time; the others do not see your times anymore then. If you give an address to be told about bookings on your booking page, it is kept with the page (and removed when you unpublish it), used to mail you, and given to somebody who booked only as part of an invitation once their time is set. You can also keep signing in on your side: a calendar file you downloaded is stored here as it was when you handed it over, and with Google signed in in your browser we receive only when you are busy, not the events and nothing that gives access to your account. For the calendars the server reads itself, we store in encrypted form on our own server what gives access to the calendar: the access key issued by Google together with your Google address, the iCal address, or the CalDAV address, user name and password (please use an app password). They are not passed on to anybody. You can remove a calendar at any time under "Calendars"; a Google access key is then revoked at Google, and all are deleted here.