Someone who has lost the ability to hear. It is one of the conditions sought be a few transabled individuals.
There are many levels of deafness, and for most, anything less than complete loss of hearing is only refered to as "Hard of Hearing".
Do not confuse "Deaf" with "deaf". The word deaf, without the capital, represents the condition of not being able to hear. The word Deaf, with the capital, represents belonging to the Deaf culture