What is the X in X-mas?
1948, shortening of bebop or rebop; as a verb, "play bop music, play (a song) in a bop style," from 1948. It soon came to mean "do any sort of dance to pop music" (1956). Related: Bopped; bopping.
The musical movement had its own lingo, which was in vogue in U.S. early 1950s. "Life" magazine [Sept. 29, 1952] listed examples of bop talk: crazy "new, wonderful, wildly exciting;" gone (adj.) "the tops--superlative of crazy;" cool (adj.) "tasty, pretty;" goof "to blow a wrong note or make a mistake;" hipster "modern version of hepcat;" dig "to understand, appreciate the subtleties of;" stoned "drunk, captivated, ecstatic, sent out of this world;" flip (v.) "to react enthusiastically." [Life Sept. 29, 1952]
: a bop musiciannoun