A fork is really just one specific case of a bigger idea: a double attack, one move that threatens two things at once, so the defender can only save one. Queens, rooks, and bishops can create double attacks too, usually by landing on a square that lines up two targets along two different lines at once.
The key safety check before playing one: make sure your own piece, sitting on that new square, isn't itself hanging to anything. A double attack that loses your own piece back isn't a double attack, it's just a blunder.
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White's queen on d1 can jump to a square that lines up both the knight and the rook at once, safely.
Which move attacks both the knight and the rook at the same time?
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