Aspects of Camera Lenses: Posterior Surface
Camera lenses are essentially the "eyes" of the camera, and just like human eyes they are complex mechanisms comprised of many parts working together. Although most of us will refer to "a lens," in the singular, they are in fact compound devices, comprised of a few lenses working together to create the image – the photo. One of these parts is referred to as the posterior lens.
The posterior lens is the lens that sits the closest to the camera body or, in other words, farthest away from whatever you are shooting. The posterior lens, the very center of which is referred to as the posterior pole, is the very last point at which the light passes as it is projected onto your camera's image sensor. The axis of a camera lens ends at the posterior pole.
The term "posterior" is derived from a field totally separate and apart from photography: biology. Generally speaking, something that is on the posterior surface is that which is facing the back of the body, such as the posterior of the arm. In reference to a camera lens, then, the posterior surface is the surface that faces (is closest to) the body of the camera.