1. The duration of one tick of the system clock on your computer
(see tick). Often one AC cycle time (1/60 second in
the U.S. and Canada, 1/50 most other places), but more recently 1/100 sec
has become common. The swapper runs every 6 jiffies
means
that the virtual memory management routine is executed once for every 6
ticks of the clock, or about ten times a second.
2. Confusingly, the term is sometimes also used for a 1-millisecond wall time interval.
3. Even more confusingly, physicists semi-jokingly use ‘jiffy’ to mean the time required for light to travel one foot in a vacuum, which turns out to be close to one nanosecond. Other physicists use the term for the quantum-nechanical lower bound on meaningful time lengths,
4. Indeterminate time from a few seconds to forever. I'll do
it in a jiffy
means certainly not now and possibly never. This is
a bit contrary to the more widespread use of the word. Oppose
nano. See also
Real Soon Now.