Steampunk is broadly speaking inspired by the 19th century and combines elements of this time period. Rather than featuring advanced electronic technology such as Cyberpunk, it generally features steam-powered technology.
The "Ministry of Peculiar Occurrences" states the following; "Steampunk is modern technology—iPads, computers, robotics, air travel—powered by steam and set in the 1800’s." 
Closely related to Steampunk and lesser Historical Sci-Fantasy, but generally now seen as sub-genre of it, is "Clockpunk" that focuses only on the clockwork elements of steampunk and in pre-European mid-14th to early 19th-century aesthetics and technology.
It's first to be officially blends of Steampunk meets Historical Fantasy, Where usually take places in Victorian to Edwardian era Western Europe and North America (or completely whole alternate universe in some stories) that contained fantasy as part of story.