As you know, when creating a calendar event you can add required guests but did you know that you can define each guest as either being required or optional?
Step 1: Add your guests to an event
Step 2: Click on the silhouette of the person icon next to their name. The figure will turn white to indicate that their participation in this event is optional. You can also use this to keep someone in the loop of a meeting as an FYI.
Kimberly Larson 