A “freezeout” is a type of poker tournament with a specific structure. Players bet and are eliminated one by one until there’s only a small number or often just one player left.
They are not allowed to re-buy or add money to their initial stack. Once a player loses their chips, they are bust and out of the tournament.
The prime example of a freezeout tournament is the WSOP Main Event, arguably the biggest and most important competition in the poker world.