In philately, a definitive stamp (sometimes called just "a definitive") is a standard stamp issued by a postal service over an extended amount of time. The counterpart to definitive stamps is commemorative stamps, which are meant to celebrate a specific person, place or thing. Definitive stamps usually have a simple design, and feature a basic object. For example, in the United States, flags are popular on definitive stamps. Although definitive stamps are limited, there can still be several different designs on definitive stamps at one time.
In the United States, definitives exist among all denominations of stamp. Currently, things like postcard rate, make up rate and global rate are all definitive. Most commemorative stamps are first class rate, but there are also definitive stamps as well, and they are what most people will get from the post office if they buy first class stamps without specifying what they want.