"Imagine if the works of Jules Verne and H.G. Wells were history, rather than fiction.". My definition of Steampunk.
Steampunk is a relative of cyberpunk and is a similar contraction, combining Steam and Punk. Steam harkens back to the late 1800s and early 1900s – where Victorian ideals of dress, manners, propriety and style were combined with the Industrial Revolution’s explosion of devices of convenience powered by steam and clockwork. Dirigibles and massive mechanical thinking engines ala Charles Babbage feature heavily. Punk has the attitude of rejecting the status quo, the current ideals and replacing it with a solid dose of rebellious self reliance. Constructions made by the self or a group rather than mass produced commercialism is a key concept here.
Some unifying elements of steampunk are Do It Yourself (also helps when things inevitably break; if you know how it went together it’s easier to fix), Neo-Victorian/ Late-Victorian aesthetic (chances are most people have garments that could fit this aesthetic that need tweaking), Retro-futurism (jetpacks et al.), Romanticism (steamy!). On this very site you can see the Royal Omnitological Society for Electrodyne Adventurers founding members, a web-app for generating cogs and another for generating gauges. If you’d like to know more, there’s the always reliable cough cough Wikipedia article on Steampunk. What I’d like to focus on, as is my want, is ridiculousness and my own intra-genre definitions.
Instead of rebelling punk, its a survivalist post apocalyptic rationale that drives this intra-genre. Typified by grime, grit, rust, cobbled-together relic-devices from lost civilisations (spoilers: us) and very smart urchins. Some of them explain how we ended up in this mess but many of them just let us surmise that, somewhen, “we done goofed.”
Things can be marvellous and adventure is everywhere. Evil is obvious and can be defeated by a swift punch to the chin, it may cackle and threaten; but rarely do they do things like break fingers to prove points, evil loves the idea of a civilised duel to show who was right. Strange locales, rose-tinted views of just about everything.
Take actual history and en-tech-ify it. Larger and more solid class divides, many more orphans, the march-of-modern-technology (read: industrial revolution) results in a depression and massive job loss rather than a wonderful age of reason and wonder (unless you’re monarchy or upper class, then bully for you).
Only one example exists to my knowledge. Thank Tesla.
I kid, this is Ged Maybury, excellent Steampunk author, having fun with the genre. Fun! It's what we're here for!
Just about anything, as long as you cover at least part of it in cogworks, gears, vents, brass or other sciencey doodaderry.