Textbooks will usually describe the word "ghetto" as a place where a minority group dominates. Unfortunately these cities and towns of living are often run down with a high crime rate. That is part of the reason Martin Luthe King addressed the problems of African Americans being forced from a "smaller ghetto to a larger one." In pop culture terms it often refers to bad living areas (whether minority groups dominate or not) and things that are of low quality.
Oprah: This fast food restraunt has the worst fries. It is so ghetto!
50 Cent: I grew up in the ghetto! Why do you think I am a rapper?
Alex Trebec: Why are my shows ratings getting to be so low? My show is not that ghetto!
Jessica Simpson: My black friends are not welcome on the farm. This run down country town is ghetto!