A Teamup Calendar administrator link is the key to the “control center” of your calendar. The default administrator link is named “Administrator” when a new calendar is created, but it can be renamed as you wish.
It is shown in the top right of your calendar:
The calendar settings are the control center for your entire calendar. Within the Settings, you can add users and groups, create shareable calendar links, and set up passwords and general calendar settings.
It is therefore important to only use the calendar administrator link when necessary.
For sharing your calendar, or allowing calendar access to other users, either use account-based user access (most secure) or create customized shareable calendar links.
Be very careful when granting administrator access to your calendar: do not share a link with the administrator permission unless you want the person who has it to have full control of the calendar.
For more details, see The Calendar Administrator Link Explained