The Deaf community uses the lowercase deaf when referring to the audiological condition and the uppercase Deaf to refer to a group of deaf people who share a culture and a language: American Sign Language (ASL). The members of the Deaf community have inherited sign language as a result of a distinct culture throughout time. They use it as their primary method of communication and also hold a set of beliefs about their connection to society and their culture. Those who are deaf may choose to identify with the Deaf community or not. Those who are hearing may also identify as Deaf, for example, the hearing children of deaf parents.
Hard of hearing can describe a person with mild to moderate hearing loss. They may choose to identify with the Deaf community or the hearing community or be in between.
Archaic and/or offensive ways to refer to those who are deaf or hard of hearing include: hearing-impaired, deaf and dumb, and deaf-mute.
(Information taken from the National Association of the Deaf, "Community and Culture-Frequently Asked Questions")
According to the National Institute on Deafness and Other Communication Disorders, "Quick Statistics About Hearing:"