Steampunk definition, according to Wikipedia:
"Steampunk refers to a subgenre of science fiction and sometimes fantasy—also in recent years a fashion and lifestyle movement—that incorporates technology and aesthetic designs inspired by 19th-century industrial steam-powered machinery. Although its literary origins are sometimes associated with the cyberpunk genre, steampunk works are often set in an alternative history of the 19th century's British Victorian era or American "Wild West", in a post-apocalyptic
future during which steam power has maintained mainstream usage, or in a
fantasy world that similarly employs steam power..."
It goes on, but that's a reasonably concise summary of a genre that can be difficult to define. When I first wrote The Tinkerer's Daughter, I had a number of agents ask for a submission. In the end, I was always rejected because they didn't have any idea how to sell it. A few of them were familiar with steampunk, but didn't consider it commercial enough to sell to a big publisher. Those who were not familiar with steampunk didn't really seem to understand it, and didn't bother asking for an explanation. I also met rejection because those who did know steampunk had very different and subjective ideas about what it should be. One agent told me I downplayed the technology too much. The machines should have played a bigger role. Another said there was too much technology and it distracted from the story.
We've had steampunk-style novels there all along, going back at least to H.G. Wells, but nobody had classified them as such. These were just considered fringe sci-fi, or worse yet fantasy, because back then, fantasy and sci-fi were two vastly different things, and the prevailing attitude was never the twain shall meet. I'm not pointing fingers because I used to feel that way myself. I hated seeing a sci-fi novel in the fantasy section, or vice versa. I wanted my sci-fi with spaceships and aliens, and my fantasy with dragons and magic. The End.
But times have changed, and steampunk has gone through a lot of phases. It has recently become a sort of social movement like LARPing and renaissance faires. For some, it has almost become a lifestyle. But still, steampunk seems to be struggling with an identity crisis. Not surprising, considering that depending on who you're talking to the genre might be considered sci-fi, fantasy, Victorian, post-apocalyptic, or western, just to name a few.
Steampunk has been slow to move into the mainstream for this reason. The most successful attempts seem to be novels one might classify as steampunk-themed romance. This isn't surprising, since romance is such a huge market and romance readers are more than willing to embrace new and different ideas based on the novelty alone. This is the same market where vampire horror, urban fantasy, dystopian and supernatural fiction all found broad acceptance over the last decade. This is a mixed blessing. The novelty factor means that more readers than ever are willing to give something different a shot. The downside is that many of those readers were introduced to the genre through romance, and without a heavy dose of it, they may be turned off. The same goes for steampunk that leans too heavily in the direction fantasy, sci-fi, or horror. Some readers will accept one but not the others. It's impossible to avoid. When I first published The Tinkerer's Daughter, one of the story's biggest criticisms was the fact that it defied certain principles of physics. Some people were happy considering it fantasy, but others wanted it to be hard sci-fi. You can't please everyone. I wanted to emulate some of the early steampunk-themed anime I had seen, but I wanted to take a uniquely western approach. That's why I opened the series in a frontier-like setting, sort of a combination between the American prairie and medieval Europe. It was a pre-industrial post-apocalyptic society of warring elves and humans on the verge of an industrial revolution. Try explaining that to someone who's never heard of Steampunk.
I left clues along the way; certain bits of knowledge that had been retained or rediscovered after the cataclysm. Certain tech that was similar to our own, but had evolved, or perhaps devolved. I can see how ten years ago, this must have made agents scratch their heads. Some of them probably still do. But that's okay, because today these stories have a chance to find an audience that never existed before. The gatekeepers -with their ledgers and marketing teams and disapproving stares- don't get to define what readers read and writers write. The definition of Steampunk will probably continue to evolve, but this time, this genre will not be defined by some anonymous board of directors in their fancy New York office tower. It will be defined by the readers.