wouldn't that be options online in stocks?
Options is another world.....
When you "short" , you sell a share or a currency BEFORE you bought it and hope that the price fall to " cover " your position . If the price go down , you win the difference between the price that you sold an that you bought after. When the price go up you lose money because you must buying for "cover" at an higher price that you sold.
That's the opposite of a Trade "long" who is the traditional trade that you hope it go up for you can sell for higher price.