Ghetto \GET-oh\ , noun;
1. A section of a city, especially a thickly populated slum area, inhabited predominantly by members of an ethnic or other minority group, often as a result of social or economic restrictions, pressures, or hardships
2. (Formerly, in most European countries) a section of a city in which all Jews were required to live
3. A section predominantly inhabited by Jews
4. Any mode of living, working, etc. that results from stereotyping or biased treatment.
Ghetto, in English, dates to the 1610's and meant "part of a city to which Jews are restricted, particularly in Italy." It comes from Italian ghetto, but before that the origins are uncertain.
A few theories:
Yiddish get, "deed of separation"
special use of Venetian getto, "foundry"
a clipped word from Egitto ("Egypt") from Latin Aegyptus (presumably in reference to the exile)
Italian borghetto ("small section of a town"), a diminutive of borgo, a Germanic word that became borough in English.
The extension of its usage from a Jewish enclave to a crowded urban are of other minority groups happened a little before the turn of the 20th century.
About 400 years before ghetto entered the language, there was another word for the same sort of thing: jewry. That word came from Anglo-French Juerie, which derived from Old French Juierie, which became Modern French Juiverie in the 13th century. In the early 14th century jewry meant "Jews collectively," and by the mid-14th century it meant "the land of the Jews, Judea".