What does the cryptic crossword clue "In which rook may fly to mate? (5,5)" mean?

The definition is "In which rook may fly to mate?". The wordplay uses a cryptic definition. Cryptic definition The answer is SPEED CHESS.

In which rook may fly to mate? (5,5)

Times Cryptic #29225 | 1 Across | 2025-05-09 flower