Jiffy is an informal term for any unspecified short period of time, as in “I’ll be back in a jiffy”. From this it has acquired a number of more precise applications for short, very short, or extremely short periods of time.
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 (approximately 33.3564 picoseconds). It has since been redefined for different measurements depending on the field of study.
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, but more recently 1/100 sec has become common.