An option contract giving the owner the right, but not the obligation, to sell a specified amount of an underlying security at a specified price within a specified time. This is the opposite of a call option, which gives the holder the right to buy shares.
A put becomes more valuable as the price of the underlying stock depciates relative to the strike price. For example, if you have one Mar 08 Taser 10 put, you have the right to sell 100 shares of Taser at $10 until March 2008 (usually the third Friday of the month). If shares of Taser fall to $5 and you exercise the option, you can purchase 100 shares of Taser for $5 in the market and sell the shares to the option's writer for $10 each, which means you make $500 (100 x ($10-$5)) on the put option. Note that the maximum amount of potential proft in this example ignores the pmium paid to obtain the put option.
看空期权（Put Options，PUTS），也称敲出期权（Knock-out Option）
什么是看空期权
看空期权又称认沽期权、出售期权、卖出期权、卖权选择权、卖方期权、卖权、延卖期权或敲出期权：是指期权的买入者拥有在期权合约有效期内按实施价格出售一定数量标的物的权利。