The name refers to the rocking action during the move: the weight is transferred from one foot to another and then back.
It is used in a number of dances, such as East Coast Swing, Zydeco, Lindy Hop, Tango.
In such cases a one or both steps the dancer may perform a certain amount of pivot turn.
The degree of rotation in the turning rock step varies with how far the dancer wants to change direction.
The stylistic difference is that in the rock step the emphasis is in the rocking action during the step, while the term break carries the meaning of the change of the direction into the opposite, i.e., the forward break changes the direction of the movement from forward to backward.