1. A subgenre of Alternate History; this generally deals with advanced technology in the altered past.
2. Steampunk is a subgenre of speculative fiction, usually set in an anachronistic Victorian or quasi-Victorian alternate history setting. Fiction in the steampunk genre is set in the past, or a world resembling the past, in which modern technological paradigms occurred earlier in history, but were accomplished via the science already present in that time period. The genre typically falls into the realm of science fiction.
I was always was fascinated with the concept of Steampunk.  Complex machines in a bygone era, powered by steam instead of electronics and computers.  Apparently, I was not the only one: