In my research and writing, I use different variations of d/Deaf to describe the people and communities I discuss. The capitalization of one letter makes a huge difference in meaning. This difference is best described by Carol Padden and Tom Humpries, who said:

“We use the lowercase deaf when referring to the audiological condition of not hearing, and the uppercase Deaf when referring to a particular group of deaf people who share a language – American Sign Language (ASL) – and a culture.  The members of this group have inherited their sign language, use it as a primary means of communication among themselves, and hold a set of beliefs about themselves and their connection to the larger society.  We distinguish them from, for example, those who find themselves losing their hearing because of illness, trauma or age; although these people share the condition of not hearing, they do not have access to the knowledge, beliefs, and practices that make up the culture of Deaf people.”

Simply put,

deaf=the physical, audiological impairment of hearing

Deaf=a culture defined by their use of American Sign Language (ASL)

There are further definitions and terminology used that you can read about on the following page–