What exactly is AIDS?

I know this seems like a stupid question, but I feel like Its easier to just ask then to google it, and yes I know google could tell me but I can’t ask my specific question. I was just thinking about cancer research campaigns, and I wondered about AIDS research. I mean, I’m sure it exists but you don’t ever really hear about it.. Is it harder to find a cure for or something? Also, what is the death rate like, I mean Is it a legitimate death sentence 100% or is it treatable? What is the difference between HIV and AIDS? If you are HIV positive will you inevitably get AIDS, or is it chance?