The term 'Be-Boppers' refers to a style of jazz music that emerged in the 1940s and was popularized by musicians such as Dizzy Gillespie, Charlie Parker, and Thelonious Monk. The term is derived from the phrase 'bop-she-bop, ' which was used to describe the fast-paced, improvisational style of the music. The crossword solution 'CATS' is an acronym for 'Cool And Tender Swing, ' which is another way of referring to the Be-Boppers' style of jazz.