In Microsoft Teams, tagging is labeling a subset of people with @mention all at once. Tags make it easy to reach out to a large number of people based on their attributes, like roles, projects, skills, location, and so on, in a single mention, saving admin's valuable time. For example, creating a tag named 'Content Team' and adding members to it calls attention to all the members associated with the tag by just mentioning the tag name in the conversation.
Managing those tags is as important as using them. There are two ways in which you can control tags and the members associated with those tags - using UI and Microsoft Graph PowerShell SDK. A user can belong to multiple tags and each tag can have a maximum of 200 members.
Please check out the following blog for more detailed information on listing and managing tags in Microsoft Teams.