A theoretical being that some philosophers use to discuss consciousness. A zombie is identical to a regular person in every way (including his behavior), except that he has no subjective, conscious experience at all. The thought experiment goes something like: "How do you know if someone is a zombie?"
Philosophers like John Searle assert that the theoretical possibility of zombies severely hinders our ability to observe and study the phenomenon of consciousness objectively.
Many materialists, however, assert that if a being was structurally and behaviorally identical to a regular person, then consciousness would result as an emergent property -- zombies cannot exist.