Baron is an ACOL convention used in response to opening 1NT or 2NT.
After 1NT: 2 This is either a raise to 2NT without a four-card major, which will pass a 2NT response, Or game forcing with slam interest with usually no five card suit
Opener bids 2NT with a minimum hand, or lowest four card suit with a maximum
After 2NT: 3 Game forcing with slam interest, usually no five-card suit
Opener bids 3NT with a minimum hand, or lowest four-card suit with a maximum