A Skewer (thrust, reverse pin) is a X-ray related chess tactic where a sliding piece, a bishop, a rook or a queen double attacks two opponent pieces on the same ray similar to a pin, except the more valuable piece, often the checked king (absolute skewer), the queen or a rook (relative skewer) is attacked directly and compelled to move to parry the check or to avoid its capture, therefor exposing a less valuable piece which might be en prise. Some programs perform not only checks at the top of their quiescence search, but also attacks to the queen by either bishop and rook, or attacking a rook by a bishop, if an exposed piece behind might be en prise.
Following composition by Ado Kraemer and Walther von Holzhausen, Magdeburger Zeitung, 1930  covers a skewer. The threat 1... b1=Q can be parried with the skewer b8=Q+, which safes white game and forces stalemate after 1.Ka8 Bh2 and sacrificing all pawns:
1K6/1P6/1kP5/3P4/4P3/5P2/1p4P1/6b1 w - -