Steampunk is a genre that typically features steam-powered machines in a world inspired by industrialized societies of the 19th Century, marked by anachronistic mashups of technology and social values. Common settings are alternate histories of 19th Century British Victoria or the American West, with technology limited to no later than the 1910s or 1920s. The Industrial Revolution is the driving force for technology and the aesthetics of the late 1800s/early 1900s is the impetus for art and fashion. (Left: The award winning Boneshaker, by Cherie Priest, prototypical Seattle-based steampunk)
The appeal of steampunk lies partly in its romanticizing a simpler technology and a sense of any indvidual being able to embark on adventures. As well, it embraces Victorian notions of progress and optimism in their science and technology. Steampunk often recasts 21st Century ideas of gender politics and race relations into the past to create a world that never was, but, perhaps, should have been.
Seattle has sometimes been called the unofficial capital of steampunk. It is home to many conventions devoted to steampunk, such as Steamposium (an annual international convention for steam punk enthusiasts) and Phil Foglio, the writer/artist of Girl Genius (see illustration to the left) and winner of the Hugo Award (science fiction's highest award) for his series of graphic novels about mad scientists in a steampunk world.
Resources:
Wikipedia: http://en.wikipedia.org/wiki/Steampunk
SteamPosium: http://steamposium-seattle.com
Seattle Steam Rats: http://www.seattlesteamrats.com/
Phil Foglio: http://girlgeniusadventures.com
Photographs: Steampunks - models Liza James and Jared Axelrod on board Baldin 60000, by Kyle Cassidy, licensed under the Creative Commons