An abbreviation for deep-in-the-money elasticity; the elasticity of an option where its value increases (for a call) and decreases (for a put) one-for-one with the underlying price. As such, it delta is one. For example, a call option with a strike price of 100, while its underlying is currently trading at 130, will have its delta equal to or approaching one (unity). A similar situation may be observed when a put option has a strike price of 100, while its underlying is currently trading at 70. In both cases, the option’s elasticity is said to be deep in the money.