Delta

Drawn from the theoretical options pricing model (Black Scholes), the delta of an option shows the rate of change in an option premium with respect to a change in price of the underlying asset or security. For example, the premium on an option with a delta of 0.5 will move by 0.5p for every 1p move in the price of the underlying. Delta can also be defined as either (i) the probability that the option will expire in-the-money, or (ii) the theoretical number of futures contracts of which the holder is either long (with a call option) or short (put option). Hedging strategies are usually based on delta ratios.