Deafness has varying definitions in cultural and medical contexts. When used as a cultural label especially within the culture, the word deaf is often written with a capital D and referred to as "big D Deaf" in speech and sign. When used as a label for the audiological condition, it is written with a lower case d.
In a cultural context, Deaf culture refers to a tight-knit cultural group of people whose primary language is signed, and who practice social and cultural norms which are distinct from those of the surrounding hearing community. This community does not automatically include all those who are clinically or legally deaf, nor does it exclude every hearing person. According to Baker and Padden, it includes any person or persons who "identifies him/herself as a member of the Deaf community, and other members accept that person as a part of the community," an example being children of deaf adults with normal hearing ability. It includes the set of social beliefs, behaviors, art, literary traditions, history, values, and shared institutions of communities that are influenced by deafness and which use sign languages as the main means of communication. Members of the Deaf community tend to view deafness as a difference in human experience rather than a disability or disease.
In a medical context, deafness is defined as a degree of hearing loss such that a person is unable to understand speech, even in the presence of amplification. In profound deafness, even the highest intensity sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, can be heard.
- Padden, Carol A.; Humphries, Tom (Tom L.) (2005). Inside Deaf Culture. Cambridge, MA: Harvard University Press. p. 1. ISBN 978-0-674-01506-7.
- Jamie Berke (9 February 2010). "Deaf Culture - Big D Small D". About.com. Retrieved 22 November 2013.
- Baker, Charlotte; Carol Padden (1978). American Sign Language: A Look at Its Story, Structure and Community.
- Ladd, Paddy (2003). Understanding Deaf Culture: In Search of Deafhood. Multilingual Matters. p. 502. ISBN 978-1-85359-545-5.
- Lane, Harlan L.; Richard Pillard; Ulf Hedberg (2011). The People of the Eye: Deaf Ethnicity and Ancestry. Oxford University Press. p. 269. ISBN 978-0-19-975929-3.
- Elzouki AY (2012). Textbook of clinical pediatrics (2 ed.). Berlin: Springer. p. 602. ISBN 9783642022012. Archived from the original on 2015-12-14.