Stefany Anne Golberg in The Smart Set:
The aesthetic movement Steampunk wants to bring the wonder back into our relationship with machines. Its tack is to fully embrace (and affect) an Edwardian orientation to the world. Though Steampunk has been a growing cultural trend for a few decades, it really came into its own in the aughts and is now a full-fledged phenomenon. Steampunks dress like the Wright Brothers and Arctic explorers. They write alternate history fantasies in which alien clones ride around in dirigibles by the light of gas lamps. Steampunks are fascinated by mechanics, and Steampunk art, jewelry, and fashion often involve gears, wheels, pulleys, and, of course, steam: a laptop computer fused with a rickety typewriter; an arcade game redesigned to look like a mini-submarine. What most defines Steampunk as a culture, however, is attitude. The “punk” in Steampunk confronts technology's alienating qualities with messy DIY defiance. The “steam” (besides its literal connotations) is almost like another word for magic: brute, utilitarian contraptions powered by clouds, and breath — ephemeral energy.
Steampunk tries to capture that Edwardian moment when steam power still ruled and the romance of technology lay precisely in the line it toed between destruction and possibility. Equally fascinated by flying machines and trench warfare, Steampunk is both optimistic and nihilistic. I like to think of this attitude as Gleehilism. It's this Gleehilism that makes Steampunk one of the defining aesthetic movements of the early 21st century.