A Ghetto, was the location were Jews during the WW2 were marginated, as the expression of an anti-semitic racial policy of Adolf Hitler that became institutionalized.
Most of the Ghettos were established all over Germany, Poland, parts of France. There the conditions for a living were extremely bad: they lacked the most essential things for a living. Many didn't have good energy and water supply. The security of the neighborhood is also compromised. Many unrest can happen and there is little to be done as authorities will not care. As leaving a Ghetto was illegal, the people escaping them were systematically executed.
Perhaps the most representative Ghetto is the nowadays Warsaw Ghetto, that serves as museum and memorial for Nazi crimes against humanity. This Ghetto once had almost half a million people living on it.
Below you can see how many Ghettos mostly in East Europe were later transformed into Death Camps:
