Jews from Germany and Nazi-occupied countries were rounded up and deported by rail to the extermination camps in occupied Poland, where they were summarily killed. The Germans attempted to disguise their intentions, referring to deportations as "resettlement to the east." The victims were told they were to be taken to labor camps, but from 1942 onward, deportation for most Jews meant transit to killing centers and then death.
Sources: U.S. Holocaust Memorial Museum