A novella is a work of prose fiction with a length between a short story and a novel. Many define a novella as between 20,000 and 49,999 words (and approximately < 100 pages). The Science Fiction and Fantasy Writers of America defines a it as being between 17,500 and 39,999 words in length[1]. In this wiki, a novella's title is usually enclosed with double quote symbols, and an example of a novella is "Of Mice and Men" by John Steinbeck.
The word novella was originally an Italian one meaning a tale or piece of news and as such was applied to the work of such writers as Boccaccio. The word novel comes from the same source[2], although the full length novel evolved many years later.