Steampunk is a sub-genre of fantasy and speculative fiction that is often associated with cyberpunk. Apart from time period and level of technological development, the main difference between cyberpunk and steampunk is that steampunk settings tend to be less obviously dystopian or lack dystopian elements entirely.
The term “Steampunk” denotes works set in an era where steam power is still widely used —think Victorian England— but with prominent elements of fantasy or science and alot less “stuffiness”. It could be the Time Machine found in the works of H. G. Wells or real technological developments (like the computer) occurring at an earlier date.
Alternate history is a popular motif where technologies like dirigibles, analog computers, or digital mechanical computers (such as Charles Babbage’s Analytical engine) are presented in an idealized light, or with a presumption of functionality. Visually, the steampunk aesthetic is often described as pseudo- or neo-Victorian, and a number of visual and musical artists have been described as steampunk.