4NT-
5C: 0 or 3 aces
5D: 1 or 4 aces
5H: 2 aces of the same rank
5S: 2 aces of different ranks and different colours
5NT:2 aces of the same colour
A bidding convention is an agreement between two players on a different meaning of a bid in the card game bridge. These agreements are made so that partners can more quickly determine which contract, with both their cards, they can win together. Often, conventions are forged together into one, which is then called a bidding system.