I never knew this, but “Jiffy” is not just slang…

Jiffy is used in different applications for various short, very short, or extremely short periods of time. In informal speech a “jiffy” means any unspecified short period of time, as in “I’ll be back in a jiffy”, but in other contexts it has more precise definitions. The word is thought to originally be thieves’ cant for lightning, though this cannot be confirmed.

The earliest technical usage for jiffy was defined by Gilbert Newton Lewis (1875–1946). He proposed a unit of time called the “jiffy” which was equal to the time it takes light to travel one centimeter. It has since been redefined for different measurements depending on the field of study.

Use in electronics

In electronics, a jiffy is the time between alternating current power cycles, 1/60 or 1/50 of a second in most countries — see alternating current.

Use in computing

In computing, a jiffy is the duration of one tick of the system timer interrupt. It is not an absolute time interval unit, since its duration depends on the clock interrupt frequency of the particular hardware platform.

Early microcomputer systems such as the Commodore 64 and many game consoles (which use televisions as a display device) commonly synchronize the system clock with the vertical frequency of the local television standard, either 59.94 Hz with NTSC systems, or 50.0 Hz with most PAL systems. Within the Linux 2.6 operating system kernel, since release 2.6.13, on the Intel i386 platform a jiffy is by default 4 ms, or 1/250 of a second. The jiffy values for other Linux versions and platforms have typically varied between about 1 ms and 10 ms.

Use in physics

The speed of light in a vacuum provides a convenient universal relationship between distance and time, so in physics (particularly in quantum physics) and often in chemistry, a jiffy is defined as the time taken for light to travel some specified distance. In astrophysics and quantum physics a jiffy is, as defined by Edward R. Harrison, the time it takes for light to travel one fermi, which is the size of a nucleon. One fermi is 10−15 m, so a jiffy is about 3 × 10−24 seconds.

Sometimes a jiffy is used as a synonym for the Planck interval, about 5.4 × 10−44 seconds, which is the time it takes light to traverse the smallest meaningful length, the Planck length. In this quantum mechanical definition, a jiffy is the shortest theoretically possible time period that can be measured within one standard deviation of accuracy. In practice, current technology can come nowhere near making this brief a time measurement.