Cradle or rock step
A forward and backward rocking step done in time with the music and with or without chiches, which is useful for marking time or changing direction in a small space. This movement may be turned to the left or right, danced with either the left or right leg forward, and repeated as desired.
Also see Hamaca.
(from batango.com (http://www.batango.com/Loomis.htm))
If you reverse the direction of the second step, so that you return to your starting position, you've done la Cunita (the Cradle, or Rock step). Don't stand with your legs apart as you do the rock; bring your feet close together at the end of each step.
(from Larry E. Carroll (http://home.att.net/~larrydla/basics_1.html))