A skewer lines up two enemy pieces on the same rank, file, or diagonal, just like a pin, but in the opposite order: the more valuable piece is in front. Forced to move out of the attack, it uncovers whatever was standing behind it, and that piece falls too.
The king is the most common front piece in a skewer, since check forces it to move immediately, no choice about it. Whenever you can line up a check with something valuable sitting right behind the king on the same line, look for the skewer.
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White's rook on h1 can swing onto the e-file. The black king can't block or capture; the queen sits directly behind it.
Which move sets up a skewer, winning the queen next move?
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