The Gulag was the government agency in charge of the Soviet forced-labor camp-system that was set up under Vladimir Lenin and reached its peak during Joseph Stalin's rule from the 1930s to the early 1950s. The camps housed a wide range of convicts, from petty criminals to political prisoners. The Gulag is recognized by many as a major instrument of political repression in the Soviet Union.

"Gułag" był systemem obozów pracy przymusowej w ZSRR, podczas gdy "łagier" to określenie pojedynczego obozu w ZSRR. Niekiedy spotyka się nieprawidłowe użycie terminu „gułag” w znaczeniu „łagier” (pojedynczy).