Vienna Gambit

The Vienna Gambit is an opening in chess by White which can cause problems for Black:

1.e4 e5
2.Nc3 Nf6
3.f4. ...

One response is 3...d5, which enables taking a pawn back from White if it takes the pawn at e5.

Often this opening speeds up the match, which makes it ideal for blitz chess and rapid chess.