What is Steampunk?

I assume that nearly everyone who comes to this website probably knows already what steampunk is, but for those that don't, I thought this would be helpful.

The problem is, though, that steampunk doesn't really have just one definition.  With that in mind, I offer a selection of them:

Wikipedia:

Steampunk is a sub-genre of science fiction that typically features steam-powered machinery, especially in a setting inspired by industrialized Western civilization during the 19th century.

The Ministry of Peculiar Occurrences:

Steampunk is an inspired movement of creativity and imagination. With a backdrop of either Victorian England or America’s Wild West at hand, modern technologies are re-imagined and realized as elaborate works of art, fashion, and mechanics. If Jules Verne or H.G. Wells were writing their science fiction today, it would be considered “steampunk.”

Steampunk.com:

Steampunk has always been first and foremost a literary genre, or least a subgenre of science fiction and fantasy that includes social or technological aspects of the 19th century (the steam) usually with some deconstruction of, reimagining of, or rebellion against parts of it (the punk).