Clicking on "teams" in the "people" section of the library will take you to a list of all the teams in your organization. Teams are a way for users to organize into groups that allow for easier sharing and collaboration.
Teams have similar access permissions to other entities in Riffyn, and as such admin access is required to add new users to a team. Other permission levels can still view the members of a team.
When sharing an entity from other places in Riffyn, you can type the team name to share with all users in the team, instead of typing individual user names.