Fork
A single piece attacking two targets at once. Knights fork best because their attacks cannot be blocked.
White to play
Nc7+
From c7 the knight touches the king and the rook at once. The king must move, and then the rook falls.
What to look for
For knights, look for two enemy pieces a knight's move apart from a common square — kings and rooks on the same colour are the classic pair.
When it applies
Any time the enemy king and a heavy piece sit near each other. A knight check that also hits a rook wins material outright, because a check leaves no time to save the rook.
How it goes wrong
The forking square has to be safe. A knight fork on a square defended by a pawn is a knight given away with extra steps.
Where it came up
Not cited in your current game.
Practise it
No positions yet. When you miss this idea in a game, the position it cost you shows up here — and in the practise set — with the answer hidden.