When you consider that an activity is finished, you can mark it as completed.Completed is a toggle option, which you activate and deactivate using the same menu option or shortcut key. A tick () specifies that the activity is Completed.
Follow-ups of attendees are completed automatically
When you are the owner of a follow-up with attendees, for example a meeting, and you mark it as Completed, the linked follow-ups of all attendees are marked as completed too. Attendees only need to complete the follow-ups where they have invited others.