Merriam dictionary defines 'steampunk' as:
science fiction dealing with 19th-century societies dominated by historical or imagined steam-powered technology
Steampunk is often characterized by the setting of the story and inventions that are fantastical and magical. Steampunk uses a lot of visual descriptions, especially when it comes to the machinery and fashion. Oftentimes, a lot of description will go into how a machine works. Supernatural elements are typically included in a steampunk story. Steampunk plots are adventure-driven stories, where machines play the part of moving the adventure along. Since there is so much action packed into most steampunk novels, the pacing is usually fast.