For a long time, drabbles were defined as 100-word stories. Sometimes you could dip into over 100 words, but the object of it was to tell a story in exactly 100. It's a deceptively simple-looking writing challenge that invites creativity through minimalism, and can be a great tool for chipping at writer's block.
Lately, that definition seems to have been lost and redefined as stories that range from 500 to even 1000 words. I'm not sure when this happened (one of my friends speculates that it might have been somewhere near the emergence of AO3), but I'm at an even greater loss for why it happened. I've even seen 500-1000-word stories not labeled as drabbles receive comments along the lines of "This isn't a full fic, it's a just a drabble." I've seen writers on Tumblr post that their ask box is open for drabble requests, and end up exhausted from writing 300-500-word stories. (Has "drabble" become a substitute phrase for a short story?) It's a little troubling, because the former example implies that short stories are somehow "lesser", and the latter shows writers being pressured to overexert themselves. (Mind, if the writer is writing over 100 words for drabbles because inspiration struck, that's fantastic, but most of the ones I've seen don't have that definition of a drabble in mind.)
tl;dr Let's bring back the original definition of drabble as a 100-word story. They're great writing challenges.