The slip jig is a solo Irish dance in 9/8 time. It is traditionally reserved for women, but increasingly being learned and danced by boys. The name also applies to the music played to accompany the dances.
It is the most graceful of the Irish dances. Dancers wear Ghillies (soft shoes), and the moves include hopping, skipping, sliding, and pointing. It is moderately difficult to learn, and is usually tackled after the reel, and standard jig.
The music has a relentless driving rhythm with stress on beats 1, 4 and 7. It can be counted in 3 sets of 3 beats, compared with a standard jig's 2 sets of 3 beats. Examples of the style are listed below, although note that there are often reel counterparts with the same name:
Although not a slip jig, Fairport Convention have a song entitled Slip Jigs and Reels.
Thanks to dharmaraja for info.