Steampunk is a sub-genre of science fiction, alternate history, and speculative fiction that came into prominence during the 1980s and early 1990s. Steampunk was influenced by, and often adopts the style of, the 19th century scientific romances of Jules Verne, H.G. Wells, Mark Twain, and Mary Shelley. Specifically, steampunk involves an era or world where steam power is still widely used -usually the 19th century and often Victorian era Britain- that incorporates prominent elements of either science fiction or fantasy. Works of steampunk often feature anachronistic technology or futuristic innovations as Victorians may have envisioned them; in other words, based on a Victorian perspective on fashion, culture, architectural style, art, etc. This technology may include such fictional machines as those found in the works of H. G. Wells and Jules Verne or real technologies like the computer but developed earlier in an alternate history.
Steampunk is often associated with cyberpunk. They have considerable influence on each other and share a similar fan base, but steampunk developed as a separate movement. Apart from time period and level of technology, the main difference is that steampunk settings tend to be less dystopian. Various modern utilitarian objects have been modded by individual artisans into a pseudo-Victorian mechanical 'steampunk' style, and a number of visual and musical artists have been described as steampunk.
Steampunk, like one who questions gender in society, is finding it hard to live within the skin that it had been created in. Steampunk doesn't just want to stay in Victorian England. It loves the idea of Dr. Steel and the Atomic Age. It pines to know its own future. Will it be like Waterworld, Tank Girl, or maybe populated by contraptions like the amazing train Doc Brown rode in on at the ending of Back to the Future III?
What's it worth? Take a look at this Steampunk price guide: sold listings for a value indication.