Generally speaking, steampunk is a sub-genre of speculative fiction that is set in the Victorian period of the late 19th century or a “Victorian-like period” where steam power is the dominant driving force of the world (instead of gasoline or other 20th century developments). The civilization may even be highly advanced with spacecraft, ray-guns, and clockwork super-computers. The writings of Jules Verne and H. G. Wells serve as the primary source of inspiration for steampunk stories, but so do many Victorian-period inventors such as Charles Babbage and Nikola Tesla. Steampunk may also incorporate elements of fantasy as well, but it is predominately set in the Victorian-period of Earth with little if any magic or magical beings (although the stories may have fantastical “magic-like” steam-powered machines).
The “punk” in “steampunk” is derived from the name of its parent genre, cyberpunk. Why is cyberpunk the parent genre of steampunk? Primarily because many of the more famous “steampunk” authors were cyberpunk authors in the 80s and 90s (Gibson, Sterling, Neal Stephenson). Steampunk also incorporates many of the same themes, atmosphere, and attitudes about technology that cyberpunk does. True steam-“punk” is typified by a rebellious attitude, and is centered around misfits and anti-heroes. Basically, “steampunk” is a cyberpunk story that replaces computers and cybernetics with mechanical computers and steam-powered devices.
“Steam fantasy”, on the other hand, is a fantasy world with steam-age elements. “Steam fantasy” may not even be set on Earth at all, but rather in an entirely unique fantasy world, such as Mythania. In this setting, many of the traditional fantasy elements may exist, such as wizards, dragons, magical races, and so forth, with the additional introduction of firearms, steam engines, flying machines, and mechanized war machines. “Steam fantasy” may also blend magical enchantments with steam-powered devices, adding a whole new dimension to the development of technological wonders. “Steam fantasy” may not necessarily be “punkish”, and technology may either be shown to be a positive influence on society or the source of endless terror and conflict, or both.
For more on the subject of steampunk and the “steampunk sub-culture”, drop by Brass Goggles or the Aether Emporium. To entertain your imagination, visit my Mythania homepage and peruse a few short stories.