This is an Acol convention. In NoTrump opennings, responder asks the lowest-ranking 4 cards suit of the opener by bidding 2 Clubs. Opener bids his 4 cards suit with maximum points, bids 2 NT with minimum hand or if the only 4 cards suit is Clubs. Convention works in the 2 NT opennings in the same way.
However this application has been abondoned with the introduction of Stayman and Transfer applications. Acol players who play Stayman and Transfer conventions apply the Baron convention in a different way. 2 Spades response to 1 NT openning is an invitation to 3 NT with 11-12 HCP or may be a slam invitation with 18+ HCP in case of 4-4 fit in any suit. Responder does not have a 4 cards major in this situation.
Opener bids 2 NT with a minimum hand, or bids the lowest-ranking 4 cards suit with a maximum hand. Responder decides the contract. Pass or 3 NT bid complete the auction; A new suit on the same level shows the continuation of 4-4 fit research; Simple support to minors invites to game; Shifting suit on the 4th level is a control showing cue-bid and slam invitation.
This application works on 2 NT opennings in the same way.