In anatomy and zoology: Situated on the hinder part of the bony brim of the orbit of the eye.Bounding the orbit behind, as a separate bone of sundry reptiles. See the noun.Lying backward (caudad) of the orbit of the eye, on the surface of the body; postocular: as, the postorbital part of the head.In entomology, lying behind the compound eyes of an insect.n. In herpetology, a separate bone which in some reptiles forms a posterior part of the orbit of the eye.