What length of story is considered flash fiction?

LOL!

Flash fiction is less than 1,000 words and fits on one page. It's extremely specific and very very short, very direct and has a specific format. Check online (start googling 'writing flash fiction', it'll give you info). Something 3,600 is a short story.

Most publications consider flash fiction to be 1000 words or less, some topping it at 500 words.

Your story's word count is typical for a short story.

Typically anything under or up to 1,000 words or so would be considered flash fiction, but I've seen works that went up to 5,000 words being classified as flash fiction pieces so I don't think the parameters are very rigid.

Definitions vary, but 3,600 words is some way above anything I've seen classed as flash fiction. So I'd say it's a short story.