What is the X in X-mas?
popular type of fast swing dance, 1938, American English, from "Jitter Bug," title of a song recorded by Cab Calloway in 1934. Probably the literal sense is "one who has the jitters" (see jitters; also cf. bug (n.)). Another sense current about this time was "swing music enthusiast." As a verb from 1938.
A devotee of swing music, esp one who dances to swing: Jitterbugs are the extreme swing addictsverb
To dance to swing music: Do you feel like jitterbugging a little bit? (1930s+ Jive talk)