Steampunk as an active sub-culture arose from the science fiction sub-genre of the same name that became popular in the mid- to late-1990s. Novels like "The Difference Engine" by William Gibson and Bruce Sterling re-imagine a Victorian age where steam-powered technology is far more advanced than it really was in the 19th century. The rollicking, fantastical adventures created by Steampunk authors fit squarely in the tradition of Jules Verne and H.G. Wells, but with the twist that modern writers know how technologies like computing actually developed and thus can retro-fit today's tech to an earlier time in an almost plausible fashion.
The central conceit of "The Difference Engine," for example, is that Charles Babbage's designs for computational machines, which in reality were never built, have been developed to usher in the Information Age a full century before it actually occurred. Interestingly, the steam-powered computers in Gibson and Sterling's novel are inspired by Babbage's designs for what he called an "Analytical Engine," widely regarded today as the first architectural breakthrough in computing, not his separate plans for a Difference Engine, which was a very powerful but ultimately non-computational calculating machine.
Did Gibson and Sterling simply make a mistake? Not likely, says Steampunk author G. D. Falksen, who guesses that the pair probably preferred the way "Difference Engine" rolls off the tongue to the clunkier "Analytical Engine." Falksen credits writers Kevin Jeter and Paul Di Filippo with coining the term "steampunk," a play on the sci-fi genre of "cyberpunk" that was popular in the 1980s and 90s.