(FINANCE) a tradable financial instrument that consists of a commitment to buy a fixed amount of X at a fixed price (known as a "strike price"). Put options are the opposite of a call option, in which ones to sell a fixed amount of X at strike.
Put options are useful to traders interested in covering risk. They guarantee a minimum price at which one can expect to sell one's holdings of X.
When the strike price of a put is less than the spot price, then it is "out of the money" and has no intrinsic value.
Buying put options is a way of shorting a stock; but it can also be used as a hedge against unpleasant surprises.