No, not "Hip-Hop Explained to Grandma" (though that would be very interesting) but more like the difference between sub-genres of rap,  like why the Dirty South sounds nothing like East Coast or West Coast and why Dr. Dre is different stylistically than P. Diddy ...

Eric Shafer of Audiotuts explains:

In the realm of popular music, perhaps no genre has been as popular in recent years as hip-hop. However, hip-hop is hardly a new phenomenon, so in this article, we’re going to take an in-depth look at its history and try to make sense of it all.

Link

From the Upcoming ueue, submitted by JKirchartz.