Answer:
The word and idea of ghettos was not born during the Holocaust era. In fact, the concept was born in 1516, in Venice, and the word comes from a combination of Italian and Jewish languages. The ghettos were primarily for Jewish minorities of the diaspora, who settled outside of their Promised Land. However, they also became the place for other such minorities. Although isolated from the main cities, and with their own systems, and with high levels of poverty, these ghettos were not used as jailing systems where people would be tortured, mistreated, or concentrated to be killed. They were simply like isolated neighborhoods where these minorities settled.
But during the Holocaust the idea changed. Hitler used the ghetto system and transformed it into the forefather version of concentration camps. Literally, ghettos like those in Poland became places of incarceration, where there was absolute poverty, lack of sanitation, and death, and these places were reserved for Jews, or people suspected of having Jewish blood. In the end, they simply became holding centers until the Jews could be sent to concentration camps.