Backward. What follows. This word is used when an organism is in anatomic position and it is necessary to describe a feature on its body so that others can understand without actually seeing the organism where something is in reference to something else. The heel is posterior to the toe. Note that posterior does not necessarily mean back. For example, on a dog, the tail is posterior to the back.

Also see superior, anterior, ventral, dorsal, cephalic, caudal, proximal, distal, medial, lateral, superficial, deep, prone, supine, plane, and region.