The term is a bit wordy, in an attempt to make it self-describing and to stress the similarity of the dancer's feet position with respect to the body as if a step with CBM was performed.
However the most important usage of this term in Ballroom dancing is to describe steps when a foot moves across the standing foot, while the torso moves in the same direction as the moving foot without rotation. CBMP is routinely used in steps taken in promenade position or outside partner step. CBMP helps to maintain dance position of the couple: CBMP allows the dancers to make these steps without shifting or rotating with respect to each other.
See also: contra body movement