Ghetto juice is a slang name for the brightly colored sugar water that can be bought for around a buck a gallon. The name ghetto juice, while somewhat derogatory is still less derogatory then calling it what it is, which is brightly colored sugar water.
While I personally find some "ghetto" snacks to be guilty pleasures, ghetto juice just gives me a headache. It doesn't even have the delicate subtly of flavor that Kool-Aid has. But, on the other hand, it is cheap at a dollar a gallon, which is cheap if you don't have tap water.