Wikipedia sez:
The term jig was probably derived from the French giguer, meaning 'to jump' or the Italian giga. It was known as a dance in 16th-century England, often in 12/8 time. During the seventeenth century the dance was adopted in Ireland and Scotland, where it was widely adapted, and the jig is now most often associated with these countries.
Huh. Now you know. Perhaps you’d like to get jiggy with it? In that case I recommend the Jig Playlist after the jump.