Directly from Wikipedia:
Steampunk is a subgenre of fantasy and speculative fiction that came into prominence in the 1980s and early 1990s. The term denotes works set in an era or world where STEAM POWER is still widely used—usually the 19th century, and often set in Victorian era England—but with prominent elements of either science fiction or fantasy, such as fictional technological inventions like those found in the works of H. G. Wells and Jules Verne, or real technological developments like the computer occurring at an earlier date. Other examples of steampunk contain alternate history-style presentations of "the path not taken" of such technology as dirigibles or analog computers; these frequently are presented in an idealized light, or a presumption of functionality. Also see Robert Sandberg's work.
Abney Park (album cover artwork) shows members dressed in steampunk outfits of the time. Also the Golden Compass book series by Philip Pullman, describes the use and interest of steampunk subculture. Also look at H. G. Wells's The Time Machine.