The boundaries fluctuate, and everyone can find an example that violates these word ranges; however, in general from the 30,000 foot height:

1-500. Flash Fiction (aka Ultra Flash Fiction)
501 – 2,000. Short Shorts (aka Flash Fiction)
2001 – 20,000. Short Stories
20,001 – 50,000. Novella (aka novelette)
50,001 – 100,000. Novel (If you’re a first-time novelist, best to be between 60-90K. And each genre has a preferable range of which you should be aware before you go around breaking the guidelines.)
100K+. Big novel (Significant investment by the publisher or to the self-publisher because of bounding choices for the book, paper quality, and the cost to transmit all those bytes that’ll eat into your set price.)
150K+. Epic Novel (Think “Lord of the Rings”, “Gone With The Wind”)

I’ve gleaned this from the number of times this question has come up, various articles and conferences, and those self-help books that all writer’s love. 🙂

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