In computer engineering, the length of time between successive microprocessor clock cycles is sometimes called a jiffy. This interval gets shorter as clock speeds increase. In a computer with a 2-gigahertz microprocessor, the jiffy is 0.5 nanosecond or 5 x 10-10. In some circles, the length of time required for one alternating-current (AC) utility power cycle is called a jiffy. In the United States and Canada, this is 1/60 second. In many other countries, it is 1/50 second.
In some publications, the term jiffy refers to 0.001 second. In others, it corresponds to the length of time required for a beam of light to travel one foot in free space; this is approximately 1 nanosecond. In still others, it refers to 3.3357 times 10-11 seconds, which is the length of time it takes a ray of light to travel 1 centimeter in free space. Perhaps the most interesting interpretation is the one suggested by Richard Tolman early in the 20th century. He considered a jiffy to be the length of time it takes a photon (light particle) to travel from one side of a nucleon (neutron or proton) to the other. A nucleon has a diameter of about 10-15 meter; a jiffy in this context is a paltry 3.3357 x 10-24 second.
The origin of the term jiffy is unknown. It is thought to have first been used in England during the 1700s, and referred to a brief but indeterminate time. But in some contexts, it is used as a put-off: the expression in a jiffy can mean "maybe now, maybe never."
Even the highly authoritative Oxford English Dictionary says "Origin unascertained." The earliest use it gives is from Munchhausen's Travels (1785): "In six jiffies I found myself and all my retinue . . . at the rock of Gibralter [sic]."
(Source: Various)