The "active tournament" is the tournament that you currently have open. Only one tournament at a time can be "active".
A tournament can be activated in several ways:
Note that when you activate a tournament that is part of a league, its league becomes the active league.
The tournament information displayed on the console reflects the active tournament.
The active tournament is managed in the active tournament panel.
A tournament will be opened read-only if either your tournament is locked or your license does not support the number of users that are on the tournament roster.