Zwischenzug

In chess, zwischenzug (German for "intermediate move") is a common tactic that occurs in almost every game: instead of countering a direct threat, which the opponent expects, one plays a move which poses an even more devastating threat, often an attack against the queen or the king. The opponent must counter that threat first, which will ideally change the situation to his disadvantage.

Borisenkov-Mezenev (diagram, Black to play), continued 1...f2, threatening to queen, which White countered with 2.Rg8, intending 3.Rf8+. But White resigned after the zwischenzug 2...Bb1! which allows Black to queen (3.Kxb1 f1=Q+ or 3.Rf8+ Bf5).

These moves are given in algebraic chess notation.