Wilhelm Reich was perhaps the first western therapist to name contact as a problem in living, but the concept has had long been present by implication in many philosophical traditions. Reich noticed that many people were able to interact very elaborately, but something very human was missing in the interaction. Contact is frequently mentioned, but not very clearly defined in his writing (or that of Alexander Lowen)-- it seems to be something that one "knows it when they feel it." In the Reich and Lowen tradition contact is biological, not just phenomenological-it is something that is felt. The slang expression "you feel me?" comes from this idea. Contact is a sensory and perceptual event--goodwill does not enter into it.
Contact implies that one is not playing a role. Perhaps it could be said that contact is the simultaneous perception of each other's substance by two or more people. Love requires contact. Contact happens on the surface, but it requires relatively unimpeded flow of feelings from the core to that surface. Though strong contact is rare in our society, it probably is the natural biological response to proximity. That is, it is an active process to stay 'out of contact.' Where contact is poor, the presence of other people tends to be irritating and to elicits defenses. It seems perhaps that there are two general ways of staying out of contact: abstraction and objectification.
*Whether the surface of the body in this context is the skin or extends beyond the skin (and involves the aura) is an interesting but distracting controversy. It should easily agreed that humans have a surface somewhere.