Hearing impairments includes people that are completely or partially deaf, (Deaf or hard-of-hearing are the politically correct terms for a person with hearing impairment).
People who are partially deaf can often use hearing aids to assist their hearing. Deafness can be evident at birth or occur later in life from several biologic causes, for example Meningitis can damage the auditory nerve or the cochlea.
Deaf people use sign language as a means of communication. Hundreds of sign languages are in use around the world. In linguistic terms, sign languages are as rich and complex as any oral language, despite the common misconception that they are not “real languages”.