Parity: Describing an in-the-money option trading for its intrinsic value; that is, an option trading at parity with the underlying stock. Also used as a point of reference - an option is sometimes said to be trading at a half-point over parity or at a quarter-point under parity. An option trading under parity is a discount option. For example, when an option's theoretical value is equal to its intrinsic value, it is said to be 'worth parity.' When an option is trading for only its intrinsic value, it is said to be 'trading for parity.' Parity may be measured against the stock's last sale, bid, or offer.