Open Tournament
When this setting is selected by the Tournament Host, players can find this game by on the Open Tournaments Page and join it until it is filled, so long as they meet the Open Seat Prerequisites defined by the tournament.
Note: Players who are invited directly to the tournament don't need to pass the prerequisites to get in. For this reason, it's a common practice to disable invite forwarding when prerequisites are used, so that players won't be able to join that don't meet the prerequisites unless the tournament creator invites them directly.