Definition of 'Short Selling'
of a security that the seller does not own, or any sale that is completed by the delivery of a security borrowed by the seller. Short sellers assume that they will be able to buy the stock at a lower amount than the price at which they sold short.
Investopedia explains 'Short Selling'
Selling short is the opposite of going long. That is, short sellers make money if the stock goes down in price.