Nowadays, "ghetto" is usually associated with urban, predominantly African-American slums and the hip-hop stars who grew up in them. But the "ghetto" story goes way back.
In Europe and the Middle East in the 14th and 15th centuries, Jewish people were forced to move to segregated neighborhoods under pressure from Catholic and Islamic authorities. These districts got a name with the establishment of an officially segregated Jewish neighborhood in Venice, Italy in 1516. It was called "the Ghetto," which literally means "foundry," because it was built on the site of a metal casting works.
Other Jewish ghettos sprang up around Europe later. They were usually overcrowded with unsanitary conditions and their residents' movements were restricted outside of the ghetto's walls. Abolished in the 19th century, Jewish ghettos returned to Europe under Hitler, but this time as holding places for Jews before sending them off to concentration camps.
Modern ghettos haven't usually been Jewish but they are always dominated by a single minority group. The communities are poor and working-class; they can be rural (like in South Africa) or urban. Oftentimes they house immigrants who have left home in search of opportunity. That was the case with the earlier American ghettos--such as the Irish and Italian ones of the early 20th century.
Now "ghetto" refers either to a certain district or to someone from a poor urban neighborhood. It can be a term of pride for hip-hop stars who brandish it as a badge of street cred--or just describe life in the 'hood: "Ghetto bird" is a police patrol helicopter, for example, and "ghetto blasters" are the handheld boom boxes so popular on sidewalks in the '80s.
"Ghetto fabulous," which is also the name of an album by rap superstar Mystikal, means going for the gaudy appearance of status without the cash to back it up (like souping up a Chevy Nova with expensive rims and a stereo system). But it also applies to a hip-hop star like Lil' Kim, who can afford the finer things but co-opts the flashy look of the "project princess" (lots of gold, leather and fur) as a means of celebrating her cultural roots.