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- Fairy chess
- Chess played with non-orthodox rules. Examples are circe, maximummers, problems with unorthodox pieces (fairy pieces) and problems with unorthodox boards (such as cylindrical boards, or grid boards).
- Flight (square)
- A square to which the black king can legally move (that is, one not guarded by a white piece, and not occupied by a black piece). If black plays a piece to one of these squares, thus decreasing the king's mobility, it is a self-block. If he moves a piece from one of these squares, it is square-vacation.
Read more about this topic: Glossary Of Chess Problems