A large, 4+lane semi-highway which runs east-to-west in southeastern Michigan. It is physically the dividing line between Detroit and Warren (in relation to Eminem's movie), as well as a number of other suburbs.
On its easternmost part, 8-Mile road runs through very wealthy areas. A few miles west, you will find the Eastland Center Mall, which is very nice, but almost completely Afro-Centric (lots of stores selling rap clothing, etc.). It's all downhill from there -- it gets better once you hit Southfield, though.
Nobody can doubt that it is a racial divide. Warren, for the most part, is almost completely white, while the Detroit side is predominantly black.
8-Mile is not cool. It's actually sleazy and boring. There's lots of strip clubs and crummy convenience stores, as well as check cashing and furniture rental places.
Warren is not entirely lower-class. Rather, it is a city with many income divides. Basically, the higher the mile number (ie. 10-Mile Road), the better the area. By 12 Mile, it's completely Middle Class, and most of 10-11 Mile is too, with the exception of a few pockets of starter homes and some apartment complexes known for their drug problems.
Once you cross 8 Mile, certain parts of the city look like war zones.