A piece is trapped when it has no safe square to retreat to, every escape loses more material than it's worth. This usually happens to a piece that wandered too far into enemy territory chasing something, and got cut off from getting back home.
Before moving a piece deep into your opponent's position, always check the way back out. If your opponent can seal off every retreat square, the piece you sent forward can simply be won outright, no combination required, just patience.
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Black's bishop wandered onto h3. Both of its escape squares, g2 and g4, are defended pawns.
Which move wins the trapped bishop?
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