In the sequence 2♣-Pass-2♦-Pass-2♥– Pass-2NT, most partnerships agree that the 2NT bid is a second negative, showing a very poor hand.
The need to make a second negative arises because an Acol 2♣ opening, unless followed by a 2NT rebid, creates a game force. Responder therefore needs a bid to keep the bidding alive without promising values.