De-Stalinzation refers to the series of political reforms that were instituted after the death of Stalin.
Key among these reforms was the roll back of the notorious Gulag system, and the end of a cult of personality in the Soviet Union.
This led to a period of cultural liberalism in the Soviet Union that would be short lived. Krushchev would be pushed back and many of the de-Stalinization policies would be reverted. This, however, gave a taste of freedom to many in the Soviet Union who had grown up under Stalin and began exposing the cracks in the Soviet system.