A fortnight is a unit of time equal to two weeks: that is 14 days, or literally 14 nights. The term is common in the British Isles and many Commonwealth countries such as Australia where many wages, salaries and most social security benefits are paid on a fortnightly basis. Fortnights are very rarely used in North America. The word fortnight derives from the Old English feowertiene niht, meaning "fourteen nights".citation needed]
The fortnight is the base unit of time in the FFF (Furlong/Firkin/Fortnight) System of units.