noun
Soviet Socialist Republic; SSR
Historical term for a constituent republic of the Soviet Union, such as the Russian SFSR or Ukrainian SSR.
ウクライナ・ソビエト社会主義共和国は、ソ連を構成する共和国の一つだった。
The Ukrainian Soviet Socialist Republic was one of the republics that made up the Soviet Union.
Refers to the Soviet Union as a whole, while ソビエト社会主義共和国 refers to an individual constituent republic.
From Russian 'Советская Социалистическая Республика' (Sovetskaya Sotsialisticheskaya Respublika), meaning Soviet Socialist Republic.