The phrase "steampunk" evokes a sense of the world of a novel described as such for people who know what the term means, and also has connotations of a certain worldview associated with it. These are traditionally dystopian societies that possess steam technology taken to a high level, sometimes in abundance throughout all cross-sections of life, and sometimes only allotted to the very highest sectors of life.
To be "steampunk" is to incorporate some or all of these elements into your tale. High-level steam-powered technology on its own does not a steampunk tale make, nor does slavish devotion to SCIENCE (yes, the capital letters were needed :P) above all else.
What does make a steampunk tale then?
Several factors might be included, truth be told. High-level steam technology, a dystopian government, and some sort of war making life a cruddy existence are all possible factors to include. Read pretty much any steampunk work and you can get an idea of what should be included. Many of them do a fairly good job of including the needed elements to have the label make sense.
With the technology in particular, I try to make it a part of everyday life without making it overly fantastic. By that, I mean no rocket-packs, personal propeller hats, or armaments that turn you inside out. Sure, some of those advances would be cool -- but do they really serve any purpose? Not so much.
Better to make the technology common but not over-the-top. That's one of my complaints about sci-fi stories in a lot of respects. The technology takes center stage over the plot and the characters, the very things that make us actually care about a story. If all we have are flashy gadgets (particularly in movies) then you don't get the same powerful story that resonates throughout generations.
I know, I know ... I'm starting to sound literary. There's something to be said for focusing on character though, seeing as enduring characters are what make fiction great.