The Literal Definition
What glasnost, orГласность, literally means is something like “openness.” That's it. It could be an openness to listen to rock music, to taking a ride on the Trans-Siberian railway, to just about anything you might have half a mind to do.
Where this word developed its power is when it came to represent an entire public policy—one that led to the change from the USSR to Russia today.
Glasnost As Policy: Gorbachev and the USSR
A bit of history is required to understand the immense connotations that this word carries today. Gorbachev came into power in 1986 and instituted a radical new strategy in the closed Communist state: He allowed open political and social discussion, without any potential government backlash for doing so. Before this point, government censorship had been a central tenet of the Soviet government in order to maintain political stability.
Why did Gorbachev implement glasnost?
This was done in an attempt to stop the rampant corruption within the Soviet government, by encouraging public oversight of government actions. The name for this policy was glasnost.
The intention of this policy was not to create overall freedom of speech, but that was the consequence: This dramatic reduction in the amount of censorship led to sudden increases in the flow of information in all aspects of Russian life. Suddenly, people were able to openly criticize the Soviet government, including many aspects that had previously been covered up such as rampant alcoholism, poor housing conditions, and many other broken promises of the Communists. Many of the more extreme Communist politicians were immediately removed from power for not supporting glasnost, while dissidents of the Soviets were released by the thousands from prison and were able to speak out openly. This increasing ferment of dissension eventually led to the collapse of the USSR; indeed, the failed coup that directly preceded this collapse was aimed at removing Gorbachev and his glasnost policy.
Now, use of the word is losing something of this connotation. Instead of solely referring to the policies of Gorbachev, it is a word that can apply to more than just that. Glasnost became intimately associated with the link between free speech and citizen uprisings against oppressive governments, and it is now used to refer to political environments other than Gorbachev's Soviet Union. This includes countries everywhere from Africa to Southeast Asia.
It has even lost enough of this political connotation that one can see it being used for rather apolitical products or purposes. An example of this is a piece of software simply called Glasnost which detects whether your ISP (Internet Server Provider) deliberately blocks or slows BitTorrent-like traffic, and thus in the minds of the coders, destroys your ability to be open with the rest of the world.
However, glasnost is still mostly used to refer to Gorbachev's particular public policy. It is difficult to use it for anything else, as the connotations are still so deeply entrenched within the Russian language. A word with a very generally meaning has been changed through cultural and political circumstance to mean something extraordinarily specific. This is an important consideration, no matter what language you're studying: What connotations does the word have, and how did they get there? Just learning words from the dictionary doesn't teach you the minutiae of meaning that means all the world for native speakers.