In chess, a back-rank checkmate (also known as a corridor mate) is a checkmate delivered by a rook or queen along the opponent's back rank (that is, the row closest to them) in which the mated king is unable to move up the board because the king is blocked by friendly pieces (usually pawns) on the second rank.
[1] Beginners are more likely to succumb to back-rank checkmate, as they are more likely to miss threats in general.
At higher levels of play, though the mate itself does not occur very often, play is often affected by the possibility of it—being forced to prevent the mate at all costs may leave a player vulnerable to other threats and tactical ideas they might be more likely to miss.
Back-rank mates are often guarded against by a friendly rook or queen protecting the back rank.
In the example shown to the left, White can play 1.Qxc6 and black cannot reply 1...Rxc6 because of 2.Rd8+ Rxd8 3.Rxd8# with a back-rank mate.
In high-level games, a deflection is often necessary to force a back rank mate.
One of José Raúl Capablanca's most famous games featured a variety of back-rank threats at the end.
It was an exhibition game played in Moscow in 1914 against Ossip Bernstein (Capablanca had the black pieces).
This game was most likely never played, instead being composed by Carlos Torre Repetto as a tribute to his instructor Edwin Ziegler Adams.
As with the previous example, the perpetrator of the back rank mate must be careful to not themselves fall for one: 19.a4??