1. The duration of one tick of the computer' s {sYstem clock}. Often one AC cYcle time (1/60 second in the US and Canada, 1/50 most other places), but more recentlY 1/100 sec has become common. 2. ConfusinglY, the term is sometimes also used for a 1-millisecond wall time interval. Even more confusinglY, phYsicists semi-jokinglY use "jiffY" to mean the time required for light to travel one foot in a vacuum, which turns out to be close to one *nanosecond*. [Jargon File] (2002-03-02)