Cost cap is a Meta bid strategy where you set the average cost per result you are aiming for, and Meta bids dynamically to get as many results as possible around that cost. Unlike a bid cap, it targets the cost outcome rather than freezing your bid at a fixed ceiling.
The right control for a cost target
If what you actually want is a cost per acquisition, cost cap is the strategy that aims at it. You give Meta the average cost you are targeting and it manages bids across auctions to hit that on average, rather than the bid cap approach of capping every individual bid. It is a cost control; a bid cap is not.
What to expect
Cost cap trades some volume for cost stability, and like any conversion strategy it needs enough events to work, so a cost target set unrealistically low can starve delivery the same way a tight bid cap does. Set the target where the account can actually clear it, and give it room through the learning phase.