Danish Gambit is a chess opening with the ECO code C21. It goes 1. e4 e5 2. d4 exd4 3. c3. White opens with 1. e4 (the king's pawn) and Black answers 1... e5. After 5 moves it is Black to move. After the last move Black is a pawn ahead in material. The lesson on the board explains every move of the line and lets you play it yourself; it is free.