The delivery date (or value date) is the date on which the actual underlying asset must be delivered (or a cash settlement made) to fulfill the terms of the contract.
The settlement and the date itself depend on the market, the underlying asset and also on whether it is traded on an exchange or in the OTC market. For example, foreign exchange options are settled on a spot basis, or Today+2; this means that delivery of the underlying asset is made two business days after the option's expiry date. In the commodity market, for example, options on Brent crude oil are settled; this means that delivery is made five business days after the option's expiry date.
The delivery date is also known in the commodities market as the settlement date.