Meaning

noun a Russian prison camp for political prisoners

originBorrowed from Russian ГУЛА́Г (GULÁG), the acronym of Гла́вное управле́ние исправи́тельно-трудовы́х лагере́й (Glávnoje upravlénije ispravítelʹno-trudovýx lageréj, “Chief Administration of Corrective-Labor Camps”), the government agency in charge of the Soviet Union’s network of forced labour camps, which was established in 1918 and formally abolished in 1960: see GULAG.

Etymology from Wiktionary, CC BY-SA 3.0