Nuala Ni Chonchuir describes the genre, also known as “short-short stories, micro fiction, pocket-size, postcard, palm-size and smoke-long stories”:
In my world a flash has about 500 words and is part poem, part story. Plot is not as crucial as atmosphere and significant detail, and, for me, language is paramount. Though short on words, the flash story is long on depth and should sting like good poetry. Punchy, succinct and surprising, the best flash will shift the reader’s heart but also keep it beating hard. Just like poetry, every word in a flash must deserve its place. Flash stories revel in musical prose. There is no room for frills and furbelows but there is for hints, implication and mystery. They accommodate the surreal and quirky well. Backstory cannot exist in flash: everything must be right here, right now. Flash thrives on punchy openings and breath-sucking endings. And, like its sister art poetry, it bears rereading very well.
Writing about John Cheever’s very short story Reunion, Richard Ford said it worked because of its “interconnected, amalgamated, shapely and irreducible self”, and this is a good analogy for flash fiction. The opening complements the ending which complements the subject matter which complements the language: everything connects and folds into a pleasing oneness.