The Concept of Gambit: Pawn offer for quick Development

"A gambit (from ancient Italian gambetto, meaning tripping) is a chess opening in which a player, most often White, sacrifices material, usually a pawn, with the hope of achieving a resulting advantageous position" (Wikipedia)

Here an example:

1. White takes an offered pawn - black gets a strong, mobile center, lead in development and well posted bishops

2. Black comes forward with his mobile pawn-center and and orders pieces in direction the of unprotected white king - white has to defend