Dracula is a novel. But what, exactly, is a novel? "Novel" is one of the loosest categories to describe literary genre out there. A novel is a work of fiction, usually written in prose (not poetry), and it's usually pretty long. Dracula definitely fits all those criteria, so we're going to call it a novel.
But what kind of novel is it? It's such a complicated text that it can fit in several different categories. There's a lot of action and a lot of risk-taking, so we could call it adventure fiction. After all, Jonathan Harker shimmies down the side of a castle over a rocky abyss to escape from blood-thirsty vampires! That's pretty adventurous. It could also be called a fantasy novel, because, hey, vampires don't really exist. But because it's about vampires, and not fairies and unicorns, it's not just fantasy: it's horror or Gothic fiction. Some folks even like to call Dracula an early work of science fiction, because of Stoker's obsession with super modern (for the time) technologies, like blood transfusions and phonographs.