Put Option

The right to sell a security at a given price (or range) within a given time period. Puts increase in value when the underlying security is going down and decrease in value when it is going up. A put option is the right to sell 100 shares of a stock or an index at a certain price by a certain date. That "certain price" is known as the strike price, and that "certain date" is known as the expiry or expiration date.