Stalinism is the means of governing and related policies implemented by Joseph Stalin. Stalinist policies in the Soviet Union included: state terror, rapid industrialization, the theory of socialism in one country, a centralized state, collectivization of agriculture, cult of personality, and subordination of interests of foreign communist parties to those of the Communist Party of the Soviet Union—deemed by Stalinism to be the most forefront vanguard party of communist revolution at the time.
After Stalin's death in 1953, his successor Nikita Khrushchev repudiated his policies, condemned Stalin's cult of personality in his Secret Speech to the Twentieth Party Congress in 1956, and instituted destalinisation and relative liberalisation (within the same political framework). Consequently, some of the world's Communist parties, who previously adhered to Stalinism, abandoned it and, to a greater or lesser degree, adopted the positions of Khrushchev. Others, such as the Communist Party of China, instead chose to split from the Soviet Union (Wikipedia page [1]) refers.
More information on the English Wikipedia page [2]: the Russian page is [3].