The slip jig is one the four most common Irish stepdances, the others being the reel, the jig and the hornpipe. It is danced in soft shoes. At one time only men danced it, then for several decades only women, and today slip jigs can be danced by any dancer, though at a competitive level they are almost exclusively danced by women. This dance is graceful and controlled, with heels very high, often called "the ballet of Irish dance". There are also traditional Irish céilí dances which are slip jigs, though these are much less common than reels and double jigs.
Although the previous paragraph states the Slip Jig was originally performed by men only, then women only, and currently by both men and women, a very different story is told in Irish dance schools. It is said originally, only men did any Irish step dancing. The women decided they should be allowed to participate in this as well, and began their own secret study and performance of the art form. The story continues when they were caught they were given an opportunity to show the men what they had learned. The dance they performed was the Slip Jig. The men were so impressed they not only allowed women to perform Irish dance, they made the Slip Jig, the women's dance and do not perform it. As you can tell this is completely different than what was reported in the foregoing paragraph. I have no documentation to prove or disprove either of these suppositions. I can state that in all the American competitions and the world competition, the Slip Jig is not offered for male competition, only for the women. That would suggest that the story the teachers told their students could very well be accurate. I think the name Slip Jig hints at this as well. It may be the women of days gone by "slipped" away to dance the jig when the men wouldn't let them do it publicly.
Because of its timing, the slip jig is longer than the reel for the same number of bars of music. In Irish stepdance competition, the tempo of 113 beats per minute is the same as other dances, but as each bar is longer, instead of dancing to 48 bars of music the dancer is only required to dance 40 bars of music (each of 21⁄2 steps). Stepdance judges prefer sliding motions with the feet and graceful movements that seem to slip across the floor.
Slip jig timing can also be used for strip the willow dances in céilidhfolk dance, although the fact that most social dancers do not dance the step limits its use in set dance and ceili dance socially. The tunes are fast-paced and lively in contrast to the slower Irish stepdance tunes.