Extermination camp
In the early years of World War II, the Jews were mostly sent to concentration camps.  However, from 1942 onward, they were mostly deported to the death camps.  They were told they were being "resettled" - sent to other places to live.  The Nazis built many of the death camps in Poland, which the Nazis controlled.  They did this because most of the people they wanted to kill lived in Poland.  Poland had the most Jewish people in the parts of Europe that the Nazis controlled.