The illegal practice of short selling shares that have not been affirmatively determined to exist. Ordinarily, traders must borrow a stock, or determine that it can be borrowed, before they sell it short. But due to various loopholes in the rules and discrepancies between paper and electronic trading systems, naked shorting continues to happen.

While no exact system of measurement exists, most point to the level of trades that fail to deliver from the seller to the buyer within the mandatory three-day stock settlement period as evidence of naked shorting. Naked shorts may represent a major portion of these failed trades.