MicroFiction is a work of fiction less than 1,000 words long, though the distinction varies between writers, critics and academics.
Works from 1,000 to 25,000 words are defined as short stories. Works between 25,000 and 40,000 words are novellas and over 40,000 they are novels. Very long novels (120,000 words plus) may be called epics, sagas or something similar.