The amount that an option's price will change for a corresponding change in price of the underlying stock. Call options have positive deltas, while put options have negative deltas. The delta can be altered for even fractional changes in the underlying stock. The terms up delta and down delta describe the option's change after a full one-point change in price by the underlying security either up or down. The up delta may be larger than the down delta for a call option, while the reverse is true for put options. See Hedge Ratio