novellas and novellettes are basically the same thing... short novels... or, from the other end, very long short stories... there really isn't much, if any difference between the la and the lette and, on some word count lists, they're considered ...
and, as is noted above, both are virtually unmarketable... the rare exceptions are small indie sci-fi or fantasy mags here and there, that will print one on occasion and literary reviews that will now and then include one that has exceptional literary merit... the main thing is, they aren't printed in book form, unless written by a famous figure or renowned writer...
here's some basic info on form, from a very good 'about.com' article:
The Novella
Novella is one term among several that have been used over the years to refer to fiction that is longer than a short story but shorter than a novel. The SFWA/Nebula Award criteria defines a novella as 17,500 to 39,999 words. In its purest literary form, however, novella usually means a mid-length work of a particular structure. The following diagram illustrates the structure of the "classic" novella; a good example of this kind of fiction is the well-known
Death in Venice by Thomas Mann.
As you can see, novellas have a very similar structure to short stories. The main difference is that novellas have a "reversal" somewhere in the rising action. A reversal is simply something that happens to change the direction of the action. It might be a setback, a decision or some other event. In addition to this main structure, novellas usually begin close to the precipitating incident, but then often skip backwards in time to fill in all the necessary background detail. Then they return to the normal flow of events. Again, this is well illustrated by Thomas Mann's
Death in Venice.
Novella versus Novelette
Another word that has been used to refer to fiction somewhere between the short story and the novel in length is
novelette. The specific meaning of this word had changed over time; at one time it simply meant a longish story or a shortish novel, at another time is was a slightly derogatory term for a short novel of very little substance. The word is not used extensively in English literature these days, but the SFWA makes use of it in its Nebula Award criteria to mean fiction of a length from 7,500 to 17,499 words, in other words between short story and novella length.
The Novel
A novel is a long piece of fiction. The actual length can vary greatly, but the SFWA/Nebula Award criteria specifies a length of 40,000 words and up. As you can see in the following diagram, novels tend to be much more complex in structure than short stories or novellas.
The actual number of reversals and almost-climaxes, setbacks and events can vary greatly. A novel may be only slightly more complicated than a short story (in fact, it is possible for a novel to have a structure identical to the short story diagram above, though it is unusual) or it may be far more complicated than this diagram. There may be only a few characters or there may be many; there are
usually more characters than in a short story, as there is more room in a novel to explore them, but there don't have to be. The falling action/dénouement tends to be a little longer than in a short story as well; with all those complications it can take longer for the writer to get the characters back to normal and show the results of the climax.
