This article discusses the differences between hearing impairment and deafness.
Hearing ability may be viewed on the continuum extending from perfect hearing on the one end to total inability to perceive any sound at the other. Most of us fall somewhere between these two extremes.
Socially, people tend to group themselves as being part of the "hearing world" or the "deaf world." In a few cases, individuals can move between these two "worlds."
A hearing impaired person who is part of the hearing world may have physical hearing that ranges from mild loss to profoundly deafened. The main characteristic is that they interact socially with speech and with hearing (often with use of some sort of hearing instrument). Among the most profoundly deafened in this group, most had relatively adequate hearing in earlier life, but lost hearing ability as a result of genetics, injury, disease or the like. Because they were in the hearing world and developed spoken language skills and all of their social contacts are in the hearing world, they continue as a hearing impaired member of the hearing world. While they may be physically deaf, they are not socially or culturally deaf. They speak and "hear" with hearing instruments and speech reading skills. This group also includes those born with little hearing who were raised/educated in the "oral method" (manual language prohibited; speechreading and speech therapy emphasized)
The socially/culturally deaf individual, on the other hand, interacts primarily with other members of the "deaf world." They may use hearing instruments or not. When used, they are used primarily for awareness of sound for safety reasons and to assist them to a limited extent when they need to interact with a hearing person. For the most part, they were either born without hearing or lost it very early in life, before spoken language was well developed. They are typically most comfortable using a manual language. Each country has it's own sign language. In the U.S. it is American Sign Language or ASL. This language is not English transmitted with hand signs. It is a bona fide language with its own syntax and other rules of use-the same as with spoken languages. ASL is a totally different language than French Sign Language or Mexican Sign Language or British Sign Language, etc. The deaf are fully able to communicate freely in ASL. Many mistakenly believe they should be able to read English just as any other U.S. citizen can. However, you must remember that English is a second language to them. Although they may be reasonably conversant with it, they will frequently have difficulty understanding-as you would if you went to the Philippines with a limited exposure to Tagalog, their native language.
In summary, deafness may be only a physical characteristic or it can signify both a physical condition with a social/cultural perspective. Hearing impairment can run the full gamut from mild loss to profound. The main characteristic that separates the hearing impaired person from the deaf person, is whether they relate primarily to the hearing world or to the deaf world.