Most commonly, CCCP is the Cyrillic alphabet acronym for the Union of Soviet Socialist Republics, or USSR. The corresponding Russian words are Soyuz Sovetskikh Sotsialisticheskikh Respublik.
The Soviet Union was a nation that existed from 1922 to 1991 and was the main antagonist to the United States during the Cold War. The union contained 15 republics that are now independent states, the largest of which are Russia and Ukraine.
Other, less common, meanings for CCCP include Combined Community Codec Pack, a collection of video coder-decoders for Microsoft Windows, Central Committee of the Communist Party and the poisonous chemical carbonyl cyanide m-chlorophenylhydrazone.