The Queens Gambit

1. d4 d5
2. c4

The Queens Gambit is one of the most well known openings, and is the second most popular d4 opening. White trades a pawn in exchange for control of the center and the diversion of blacks pawn away from the center. Sharp queen-side play play and king-side castling is common if black should accept the gambit. More common is declining the gambit by instead supporting the d4 pawn with either the knight or one of the pawns on the c and e files leads to more closed positions. However, the opponents skill and knowledge of the game must be taken into account when playing any gambit--move that work wonders on amateurs are often inside jokes to players with considerable experience. You would be well advised to play moves you know to be risky against players with lower strength than yours, and to explore many possible continuations of the openings you plan to have in your repertoire.

Trap in the Queens Gambit Accepted
Trap in the Queens Gambit Declined

Black to play and mate in 2