Glasnost was one of Mikhail Gorbachev's policies introduced to the Soviet Union in 1985. It can be read as 'openness'. Under Glasnost the people were told a large amount about the horrors committed by the government when Stalin was in power. Glasnost gave new freedom to the people, such as freedom of speech, which was a radical change because control of ideas had previously been a central part of the Soviet system.
Thousands of political prisoners and many dissidents were released in the spirit of Glasnost.
See also Perestroika.