A language supports some data type as first-class when the objects of the type can be created and used as data at run time. First-class data can be kept in variables, and passed to and returned from functions. In dynamically typed languages, first-class data can also have its type examined at run-time.
The U.S. Postal Service class of mail that provides the most timely delivery and is therefore the most expensive class, outside of express service. Occasionally, a direct mailer will choose to use first class for speed or impact purposes, instead of the usual standard service class. By law, invoices must be sent first class.
The highest class of service, available on most aircraft.
adj. of a first class match.
Most aircraft have at least some first class seats up front, which offer much more room and upgraded cabin service, meals, etc.
In database modeling, a first class item is one that has an identity independent of any other item. The identity allows the item to persist when its attributes change, and other items to claim relationships with the item.
First Class is a rank attainable by a Scout in the Boy Scouts of America (BSA), and ranks above Second Class and below Star. A Scout can work on the requirements for the Tenderfoot, Second Class, and First Class ranks at the same time, but must earn them in sequence. The badge is awarded when the Scout completes requirements in the areas of Scoutcraft, physical fitness, citizenship, personal growth and Scout Spirit.