a former communist country in eastern Europe and northern Asia; established in 1922; included Russia and 14 other soviet socialist republics (Ukraine and Byelorussia and others); officially dissolved 31 December 1991
"The collapse of the USSR marked the end of Cold War tensions between the West and the communist bloc."
Initialism of Union of Soviet Socialist Republics.
"The textbook explained that the USSR was an initialism standing for the Union of Soviet Socialist Republics."