Used in sciences to measure extremely quick events, where accuracy matters. Modern processors operate at speeds measured in nanoseconds.
Pro Tip 2/3
Literal Sense
Remember that in technical contexts, 'nanosecond' strictly means one billionth of a second. Data travels through optical fibers at milliseconds, not nanoseconds.
Pro Tip 3/3
Not for Duration
Though very short, it's not used to express duration in common human experiences. He hesitated for a moment, not a couple of nanoseconds, before replying.