www.irelandseye.com says that:
The lighter jig is a faster dance than the jig, slip jig and heavy jig. The double jig is one of the most popular Irish dances. It commences with the rising step, one of the first steps taught to beginners. The right foot is lifted about 12 inches off the floor, the person hops on the left, while the right is lowered to tap the floor and then each foot in turn is lifted and lowered. This action is repeated three times to one bar of music.
If you could see me trying this at home, you'd laugh.