short sale

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The sale of a borrowed security in anticipation of making a profit by repurchasing it after its price has fallen.
• noun An investment in an exchange-traded fund or derivative security whose performance is inversely related to that of a particular index.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun real estate A property sale negotiated with a mortgage company in which a lender takes less than the total amount due.
• noun investments A sale of a security that one does not own, delivery obligation met by borrowing the security from another owner.
• noun economics A sale of a financial security, commodity, or other good that one does not own with the contractual obligation to make delivery of the good to the buyer at a date in the future.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun sale of securities or commodity futures not owned by the seller (who hopes to buy them back later at a lower price)