The term jiffy refers to a brief, usually unspecified, interval of time . In scientific and lay applications, it can refer to any of several specific time spans. The most common interpretation is 0.01 second.

In computer engineering, the length of time between successive microprocessor clock cycle s 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 second. In a machine with a 3-gigahertz microprocessor, the jiffy is 0.333 nanosecond (3.33 x 10 -10 second).

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."