According to the likes of Kindlepreneur, word count categories fall as:

Novel: 40,000+ words (though you’re better off above 50,000 words)

Novella: 17,500-40,000 words

Novelette: 7,500-20,000 words

Short story: 1,000-10,000 words

Flash fiction: 1-1,000 words

Writers Digest suggests:

Short stories range anywhere from 1,500 to 30,000 words

Novellas run from 30,000 to 50,000

Novels range from 55,000 to 300,000 words

The SFFWA suggests:

Novel 40,000 words or over

Novella 17,500 to 39,999 words

Novelette 7,500 to 17,499 words

Short story up to 7,500 words

The Author Learning Center suggests:

Novella 20,000 and 49,999 words

Novelette 7,500 to 19,999 words

Short story 1,000 to 7,500 words

Flash fiction 1,000 words or less

Jericho Writers suggest:

Short story: over 1,000 words, usually less than 10,000.

Novelette: 7,500 to 19,000 words.

Novella: 10,000 to 40,000 words.

As you can see, the numbers are somewhat fluid, depending on the fiction genre, but none of them liken any genre to microfiction. It seems by these numbers that microfiction could be the traditional term flash fiction.

Thoughts?