Union of soviet socialist republics has 2 different meanings across 2 categories:
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
A confederation of nominally independent socialist republics led by the Russian SFSR and partly Azerbaijan SSR (Transcaucasian SFSR) from 1922 to 1991.