The Congress of the Communist Party of the Soviet Union (Russian: съезд КПСС) was the gathering of the delegates of the Communist Party and its predecessors. According to the party statute, it was the supreme ruling body of the entire Communist Party.
The most significant for the purpose of this wiki was the 20th Congress of the Communist Party of the Soviet Union.
More information, and a list of congresses, on the English, Russian and other language Wikipedia pages.