Where did the names of some of our modern music genres originate?

Other than Pop and Gospel, where did the names of modern genres of music come from and when? For example, where did the word "rock and roll (which would go onto be just rock)" originate from in terms of using it as a musical genre for artists such as The Beatles, Queen, and Elvis Presley? These are some of the ones I'm most curious about:

1. Rock and Roll
2. Rap
3. Country