Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...dxc4
This move captures the gambit pawn. Since the Nc3 is exposed to attacks by the b-pawn, black can often safely overextend with moves like a6 and b5 to hold to the c-pawn in this line. Also, there is a hidden trap on move 5 that many white players have fallen into. It will be explained later.