Continuum. Coma is the deepest form of loss of consciousness (loc), in which no responsiveness to the external environment exists. This can be reversible. Technically a concussion with loc means a momentary coma has occurred but the term is rarely used in that circumstance. Simple loc means loss of awareness to some external stimuli with preserved responsiveness to noxious stimuli.
Coma. In both situations there is loss of consciousness, however when we label a patient as being in coma, we usually imply that the loss of consciousness has been there for a considerable period of time, gnerally several hours to days or sometimes weeks.