the difference between a novella and a novel
Like they will say that a novel is a story of 40,000 words or more, a novella is 20,000 to 40,000 words, and anything shorter is a short story. As far as I know there's no standard in the publishing business, though. These are just ballpark numbers.
Fiction refers to a story containing imaginary or made up events. A novel refers to the length of a work of fiction. It's usually considered the longest form of literary prose.