A combination employed by a player with a losing position which converts his position into a win or draw. Such a combination is generally considered to be either avoidable by the opponent or the result of luck.
A combination played by a player who has a `lost' game - usually involving a trap which the opponent could avoid but doesn't - and the `lost' game is saved.
A ruse by which a player in a losing position tricks his opponent, and thereby achieves a win or draw instead of the expected loss.