Fortnight

A fortnight is a unit of time equal to 14 days (2 weeks). The word derives from the Old English: fēowertyne niht, meaning "fourteen nights".

Fortnight and fortnightly are commonly used words in the English-speaking world. Some wages, salaries, and social security benefits are paid on a fortnightly basis; however in North America it is far more common to use the term biweekly. Note that neither of these terms should be confused with semimonthly, which results in exactly 24 pay periods (12 months × 2), instead of the 26 or 27 (≈52 weeks ÷ 2) of fortnightly/biweekly.

Astronomy

In astronomy, a fortnight is half a synodic month, the mean time between a full moon and a new moon (and vice versa). This is equal to 14.77 days.

In other languages

In many languages there is no single word for a two-week period, and the equivalent terms "two weeks", "14 days" or "15 days" (counting inclusively) have to be used.