Delta (also neutral hedge ratio)

The percentage of the price movement in the underlying stock that will be translated into price movement in a particular option series. For example, a delta of 50 percent indicates that the option will move up (down) by one half point for each 1 point rise (decline) in the underlying stock. Call options have positive delta; put options have negative delta. Deltas increase as the stock price rises and decrease as the stock price declines. The delta is also an approximation of the probability that an option will finish in the money.