Definition: Gambit is an Italian word which invariably applies to the opening. It involves an early sacrifice of material.
A player offering a gambit sacrifices at least a pawn to achieve a positional advantage like a lead in development or a stronger center, in the hope that it will translate into superior attacking chances. The sacrifice is usually speculative, but is not easy to refute.
See the King's Gambit (1.e4 e5 2.f4) for an example. The Queen's Gambit is not a true gambit, because the Pawn can't be held.
