Coma

Coma, from the Greek word koma, meaning deep sleep, is a state of extreme unresponsiveness in which an individual exhibits no voluntary movement or behavior. In a deep coma, stimuli, even painful stimuli, are unable to effect any response. Normal reflexes may be lost.

Coma lies on a spectrum with other alterations in consciousness. The level of consciousness which you, the reader, are currently enjoying is at one end of the spectrum, while complete brain death is at the other end of the spectrum. In between are such states as obtundation, drowsiness, and stupor, which all allow the individual to respond to stimuli, though such response may be brief and require a stimulus of greater than normal intensity.