Birdland is a jazz club located in New York City. It was founded in 1949 by the saxophonist and impresario Charles Mingus, and has been a major venue for jazz music ever since. The term 'BOP' is an acronym for bebop, a style of jazz music that originated in the 1940s and is characterized by fast tempos, complex harmonic structures, and improvisation. BOP is also used as shorthand for Birdland, which is why it is one of the solutions to this crossword puzzle.