Short story
A fictional prose narrative shorter and more focused than a novella – usually deals with a single episode and often a single character. Length is generally between 2,000 and 10,000 words.
Novella
A fictional prose narrative often set in a brief period of time, such as a day, week, or month. A novella often concentrates on character study. Length usually around 17,501 to 40,000 words
Novel
A fictional prose narrative of considerable length, usually having a plot that unfolds by actions, dialogue and thoughts of the varied characters. Length 40,001+ words

