“I’ll see you soon.” “We’ll be there in a few.” “Be right there!” All of these are vague promises that you’ll be arriving at a particular place in a short period of time, but one similar phrase, “be there in a jiffy,” isn’t quite so vague. It’s been adopted as an idiomatic phrase that implies you’ll be there shortly, but “jiffy” actually refers to a defined period of time.
A jiffy is a concrete, measurable unit (that still varies, depending on the context). Some scientists use “jiffy” to denote a very, very tiny amount of time. To physicists, a jiffy is how long it takes for light to travel one femtometer (a millionth of a millionth of a millimeter). Femtometers are used to measure things smaller than an atom, so you can imagine how short a jiffy is. In electrical contexts, “jiffy” is used to measure the length of a single cycle of alternating current, where one jiffy equals 17 milliseconds. In computer science, “jiffy” is a variable term, equaling anywhere from one to 10 milliseconds.
There are many such terms that are far more specific than common usage indicates. Promising you’ll be back in a “few shakes,” for instance, is pretty impossible. In the world of physics, a shake is a unit used to measure one step of a nuclear chain reaction that equals 10 nanoseconds (10 billionths of a second). While these words have specific meanings in a scientific or technical context, they’ve been adopted as idioms. While you may not be traveling at the speed of light in a jiffy, folks will still understand your intent.
