What's the difference between rock and pop (music genres)?

Rock has more electric guitar and heavier percussion than pop does. "Pop" actually means popular, as in popular music. But, I think pop has become it's own genre, even though some people still think of it as "popular music". Hilary Duff is pop/dance, Aly and Aj are pop, Avril Lavigne is pop/rock or rock, and Ashlee Simpson is pop/rock. The Jonas brothers are punk/pop, Miley Cyrus is pop/rock. Hope this has helped!