Total number of shares of a security that investors have sold short and that have not been repurchased to close out the short position. Usually, investors sell short to profit from price declines. As a result, the short interest is often an indicator of the amount of pessimism in the market about a particular security, although there are other reasons to short that are not related to pessimism. For example, hedging strategies for mergers and acquisition as well as derivative positions may involve short sales.