The /v1/teams endpoint lists all teams in your account. Not all plans have access to the teams feature, if you do not have access to teams this endpoint will return a 200 OK response with an empty teams list.
Team ID 1 is the default company team, and always includes all users in the account.
In the Follow Up Boss UI teams also have a unicode icon associated with them, this is currently not available via the API. Please use the Admin -> Teams UI in Follow Up Boss to edit team icons.