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)