As of Dec. 31, short interest fell to about 8.676 billion shares, compared with 8.85 billion shares as of Dec. 15.

Investors who sell securities 'short' borrow shares and then sell them, expecting the stock to fall so they can buy the shares back at the lower price, return them to the lender and pocket the difference.

Shorting can also be part of a hedging strategy.

(U.S. markets team; +1-646-223-6344)