What is the difference between writing the word deaf with a lowercase d or with an uppercase D?

Lowercase "d" in the Word "deaf" represents people who cannot hear without assisted hearing devices or cochlear implants. However, uppercase "D" refers to the Deaf culture. So, you could say, "I'm deaf, but I'm not Deaf," which would mean that you can't hear, but you still associate mainly with the hearing population. You're audiologically deaf, but not culturally Deaf. This is mainly for people such as Late-Deafened Adults who grew up hearing and then lost their hearing as an adult. Many if not most choose to remain in the hearing culture.