Fool's Mate
Fool's mate, also known as the "two-move checkmate," is the quickest possible checkmate in the game of chess. One example consists of the moves leading to the position shown...
The fool's mate received its name because it can only occur if White plays extraordinarily weakly, i.e. like a fool. Even among rank beginners, the mate almost never occurs in practice.
The same basic mating pattern may also occur later in the game. There is, for instance, a well-known trap in the Dutch Defence which occurred in 1896 between Frank Melville Teed and Eugene Delmar that runs 1.d4 f5 2.Bg5 h6 3.Bf4 g5 4.Bg3 f4; it seems that Black has won the bishop, but now comes 5.e3 (threatening Qh5#, the basic Fool's mate idea) 5...h5 6.Bd3?! (6.Be2 is probably better, but this move sets a trap) 6...Rh6? (defending against Bg6#, but...) 7.Qxh5+! Rxh5 8.Bg6#...
A similar mate can occur in From's gambit (Bird's opening) 1. f4 e5 2. g3 exf4 3. gxf4?? Qh4#...
More generally, the term fool's mate is applied to all similar mates early in the game; for example, 1.e4 g5 2.d4 f6 3.Qh5#
Even more generally, the term "Fool's mate" is used in chess variants for the shortest possible mate, especially those which bear a resemblance to the orthodox chess fool's mate. Fool's mate in progressive chess, for example, is 1.e4 f6 2. Nc3 g5 3. Qh5#