I believe that 'complete' is a better description than merely 'short'. Anyone can see at a glance that a story is short. It is clearly not a novel. It has eight or ten or maybe twenty pages, rather than two or three hundred. But that doesn't make it an extract or a chapter of a bigger piece. It must be entire within itself. A miniature novel, if you like.
This is why shorter-length fiction is so challenging. You cannot waste words. Everything counts. You have to entertain as much as a novelist does, but in a much smaller time span. A short piece is often a simple snapshot of the main character's life, but it must still have a valuable opening, tension-building middle and satisfying ending. All in a couple of thousand words or even less.
If it reads as incomplete, then you have not succeeeded, whereas a novel can be incomplete even after fifty thousand or more words. There is still space to move the action on and bring in surprises, even new characters as long as they are not central to the plot. You can write another thirty to fifty thousand words and the lengthof the novel will be acceptable.
But short stories need to be whole within a far tinier margin. It's a massive challenge!