A term that has two meanings in poker.
A “cap” is a limit on the amount of bets and raises that is allowed in a betting round. Most poker games have a cap of 4 bets (which refers to one bet and three raises). That is when the action ends and the next card must be dealt unless there is a showdown.
Some online poker rooms now offer “Capped” games. In these games, there is a Cap on the amount the player can bet during any hand. So, despite still buying in for 100bb like in a typical ring game, you can be playing in a 40bb CAP game. Once the cap has been reached, you’re effectively all-in. Capped cash games are basically the same as playing shortstacked, so the decisions are a lot more straightforward.