D/deaf is just a more inclusive term. The differences between D and d can vary depending on who you ask. Some say D means born deaf / deaf pre verbally whereas d means deaf later in life, D is also more used to reference the community and those who are active in it (ie: Deaf community) whereas d is referenced towards those who don’t have a major Deaf identity or don’t involve themselves within the culture / community. D can be used towards people whose first language is sign, and d can be used towards those who lipread and speak English natively. D can be used to reference the deaf person, whereas d can be used to medically describe deafness. Some will say all of this is accurate, and I am of that opinion. I’ve heard (haha) all of these answers depending on who I’m talking to and where they are from.
‘Big D’ and ‘Small d’ in the Deaf Community
Lots of different opinions on the subject, but in very simple terms…
deaf = medical diagnosis of hearing loss
Deaf = cultural and linguistic identity