Cyberpunk is a sub-genre of science fiction literature that emerged in the 1980s.  Cyberpunk is often noted for its marriage of "high tech" and "low life" as themes.  The central characters are often rebels, cyborgs or hackers navigating  hyper-media and technology-saturated worlds.  Among the first cyberpunk novels were William Gibson's Neuromancer and his other Sprawl Trilogy novels.  The central thematic concern of this genre is the impact of a technology-driven society.  The settings are post-modern, dystopic communities where the social structure has been drastically altered by technology and corrupt corporations.  Artificial technology and the altering of the body are also common themes.  Human bodies are altered to include prosthetic limbs, and computers are sometimes connected directly to the brain.  Cyberpunk challenges human conceptions about what is real and what is unreal, how technology is related to biology, and how the body and mind are related.  Cyberpunk writing is dark, often patterned after private eye novels and film noir.  Even the protagonists are not true heros, but more "anti-heroes," which is what the "punk" part of the term refers to.  Cyberpunk literature has eventually been re-imagined in film, animation and video games.  Often considered the first cyberpunk movie, Ridley Scott's Blade Runner (1982) was based Philip K. Dick's novel Do Androids Dream of Electric Sheep?  

Helpful links on the history of cyberpunk and its influence:                     

The Cyberpunk Project

http://project.cyberpunk.ru/

Cyberpunk Review

http://www.cyberpunkreview.com/what-is-cyberpunk/

Wikipedia: Cyberpunk

http://en.wikipedia.org/wiki/Cyberpunk