"I'll be back in a jiffy"
Jiffy is an informal term we use for a short unspecified period of time. But it has taken on more precise applications for short, very short, and extremely short periods of time.
Though the word goes back to 1785, the word's origin is unclear. One possibility is that it was a "thieves' cant" for "lightning." Thieves' cant (AKA Rogues' cant and peddler's French) it was a secret language (a cant or cryptolect) which was used by thieves, beggars and hustlers of various kinds in Great Britain and to a lesser extent in other English-speaking countries. It is now mostly obsolete, and is largely relegated to the realm of literature and fantasy role-playing.
One technical usage for jiffy was defined by Gilbert Newton Lewis (1875–1946) who proposed a unit of time called the "jiffy" which was equal to the time it takes light to travel one centimeter (approximately 33.3564 picoseconds).
In electronics, a jiffy is the time between alternating current power cycles, 1/60 or 1/50 of a second in most mains power supplies.
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 computing, a jiffy was originally the time between two ticks of the system timer interrupt - which is not an absolute time interval unit, since its duration depends on the clock interrupt frequency of the particular hardware platform.
The term "jiffy" is sometimes used in computer animation as a method of defining playback rate, with the delay interval between individual frames specified in 1/100th-of-a-second (10 ms) jiffies.