What describes a person who has severe to profound hearing loss and cannot use residual hearing functionally?

The term that best describes a person who has severe to profound hearing loss and cannot use residual hearing functionally is "Deaf." This classification is used to signify individuals who experience a significant loss of hearing, such that it greatly limits their ability to hear sounds and spoken language, regardless of any residual hearing they may possess.

In the context of the audiological spectrum, "Deaf" indicates that a person is part of a unique community and cultural group that communicates primarily through sign language, understands the nuance of visual communication, and often shares common experiences and values related to their hearing loss. This cultural aspect is distinct from merely having hearing impairment or being hard-of-hearing, which may still allow for some level of functional hearing or reliance on auditory cues in communication.

Hearing impairment refers to a broad range of hearing loss, including mild to moderate losses, and does not specify the inability to use residual hearing functionally. Hard-of-hearing individuals may still rely on amplified sounds or assistive devices, making them different from those who have profound hearing loss. Deaf culture involves the social beliefs and behaviors of the Deaf community, but it is the condition of being "Deaf" that defines the specific level of hearing loss mentioned in the question.