How short is short?

I currently have to two novels working in my brain as well as a short story. However as I delve into writing short stories there is some confusion. How short is a short story? I have seen flash contest for 500 word stories. That boggles my mind. I did find a contest for 1,500 words. I wrote a 1,500-word story. The issue seems that I don’t seem to hit my stride until around 700 words. The first 1,500 words are stiff, according to my beta reader (my husband Jarrod). However, I wrote the character as stiff in the beginning. Is the stiffness from me or the character? I found it hard to get my point across in so few words. Yes, writing 750, a day has stymied me, but I wasn’t trying to tell half a story in those 750. I will have to see, I am submitting it to this contest. The deadline is November so I have time to refine and sharpen the story. Wish me luck!