People often ask me what makes a book steampunk.
There are so many possible answers for that, I rarely know where to start. So let me try to break it down for the uninitiated...
1) Power is steam-generated. But within that, there can be seriously advanced technology. (This is usually a requirement for steampunk. Otherwise where does the steam part come from?)
2) Scientists. They can be good. They can be evil. But there is usually at least one in there somewhere--often an inventor or researcher. (These are the people who are trying to change the world. They tend to think they're doing the right thing--regardless of which side they're on.)
3) Gadgets. This goes with the above. There are gizmos in steampunk. Things that we don't use in our every day world. Rayguns. Monocular. All manner of clockworks--both intelligent and not. (They are shiny. People like shiny things. Thus...gadgets. Pretty much if you can imagine it, you can probably squeeze it in there.)
4) Airships. These might not be strictly necessary for steampunk, but damn they're pretty. With the world running on steam, there aren't planes like we're used to. And as good as trains and boats are, they're not quite the same.
5) Victorian sensibilities...or not. More often as not, there's an alternate history aspect to steampunk, so it can go either way. However, there's usually at least a nod from someone about what is proper and acting like a lady. (I tend to go for the Miranda Lambert variation of being a lady. All it requires is "hiding your crazy"--most of my characters are good at that. And the others couldn't give a hoot about propriety.)
6) Brass. Actually a lot of metals, but brass is a big one. Remember the shiny things from above? Yeah. That. On repeat.
7) The look. Goes with the brass and the shiny. Steampunk in a lot of ways is about dichotomy. Think HG Wells' Time Machine. On the surface, things are all shiny and pristine, but underneath there's a darker, grimy, gritty layer.
8) The clothes. Oh my, the clothes. It's like Madonna meets Queen Victoria. Undergarments become overgarments, and your bustle skirt doesn't have to cover your knees much less your ankles...but it can if you want it to. There's leather and lace and silk and freaking burlap! It's like the gadget thing taken to an extreme--if you can imagine the clothes, someone, somewhere in steampunk would probably wear it. (And the brown thing is a myth. It's common in steampunk cosplay because of the whole brass thing, but it became common because most early photography has a sepia tone to it that made everything look brown. Don't be afraid of color.)
9) The punk. Steampunk is very political in nature. It's stories that take an issue and drag it kicking and screaming into the light to be dissected. It's subversive and awesome.
10) The people. Because of all the above, steampunk characters don't have to fit a standard mold. Your heroes don't have to be alphas (especially if your heroine is). None of your women have to be meek, mild, damsels-in-distress. All of them can be more than what their situations would dictate in reality. Make them bold.
So yeah. There's my short brush up on what makes something steampunk. Does it have to be all those things? Nah. Can there be magic? Sure! But for myself, I see that list as a pretty solid place to start.
What about you? What do you think when you hear "steampunk?"