In chess, a windmill (or seesaw)[1][2] is a tactic in which a piece repeatedly gains material while simultaneously creating an inescapable series of alternating direct and discovered checks.
Because the opponent must attend to check every move, they are unable to prevent their pieces from being captured; thus, windmills, while very rare, tend to be extremely powerful.
The bishop typically sits on the long diagonal (see Fianchetto), while the rook moves to the seventh (White) or second (Black) rank and checks the king, who is forced to the corner due to a friendly piece (usually a knight, but it can also be another rook) blocking it.
The rook then moves back to its original spot, and the process repeats until no more pieces can be captured.
The game continued from the diagrammed position as follows: Black sacrifices his queen in order to initiate an attack.