Flash fiction can be as short as you like. It can't be over 1000 words. The jury is out on whether to include the title in the wordcount. But you can't cheat and use a title that takes you seriously over the wordcount.
Microfics are tiny - usually under ten words.
Drabbles are a particular form of flashfic where a specific wordcount is adhered to - 100 for a true drabble, and then there are double drabbles, etc.
Even if it is intended to form part of a longer work, a flashfic should be able to stand alone, without explanation.
Some of my flashfic has already been published online in a 'zine' . My pen name for the zine is J.E.Mountney. (You may ask, but the answer is complicated and not really worth your time). Once it is available for re-publication, I shall upload it here. Meanwhile, go to the flashfic zine, details of which can be found here.
Most of my flashfics were written in response to prompts from various writing groups. These are a wonderful way to study other peoples' techniques, get constructive criticism, improve your writing in a supportive environment and just generally make friends. One such group was the way I found my beta group, but other people in that and other groups, have been enormously helpful.
One of my friends tells me she misses the days when the writing circle met in the village hall and retired to the pub afterwards, to sit by a roaring fire and drink together. Frankly, I think that's overrated. With the advent of the online group, there are a number of benefits to be observed:

Prompts are a brilliant way of getting you to think about things you would never otherwise have noticed and for forcing you to get to know characters or places in a longer work, as well as inspiring 'one off' pieces.
Sometimes they generate their own 'plot bunnies' which start to beg for carrots and gnaw at the door of the hutch. They can break down writer's block (something I have never suffered from). On the other hand, as a way of wasting time and not getting on with the novel in hand, they have no equal (unless it is the building of websites).
A few of my flashfics are also fanfic in that they are responses to prompts in a community which exists to encourage people to roleplay using characters from books or films. I did several flashfics, for the same community, about one of my original characters. These are naturally now part of the material I am unable to show you.
Leanne and Karen, with other fics that might some day form the basis of a novel.
Sundry flashfics.
Trickery - a short fantasy
The Cats - for children
The helpful Hedgehog - for young children