The Deaf, deafened and hard of hearing are all very distinct groups.
deaf [small ‘d’]: a term used to refer to a person with little or no functional hearing. It may also be used to refer to those who are audiologically deaf but do not identify with the Deaf community.
Deaf [big ‘D’]: is used as a sociological term referring to those individuals who are audiologically deaf or hard of hearing who identify with and consider themselves a part of the culture, society and language of deaf people based on the use of sign language.
deafened (also known as late-deafened): is used to refer to those people who lose all their hearing later in life and have been raised in a culture of spoken, written communication.
D/deaf: is used as a collective noun to refer to both those who identify with Deaf culture and those who do not.
oral deaf: a deaf person whose preferred mode of communication is verbal and auditory. An oral deaf person who uses both speech and ASL may be considered a member of the Deaf community.
hard of hearing: a term used to refer to a person whose hearing loss ranges from mild to profound and whose usual means of communication is speech.
hearing impaired: a term most often used by the medical community but not accepted by the Deaf community as it emphasizes the disability or problem.