A tag is a keyword or term assigned to your guests. Tags make it easy to categorize and organize your guests - they are a powerful feature and can be used for a number of different things:
Easily filter and export reports by tag
Create custom email audiences by tag
Filter guests by tag when creating your seating chart
Merge tag details added to a guest into an email
Filter check-in to guests with specific tag(s)
Invite certain guests to a secondary event
Ask certain guests a custom question
For detailed steps on how to tag invitees, check out this guide.