One nanosecond compares to a second the same way one second compares to 31.71 years. It's such a tiny amount of time that it's almost impossible to imagine. Some scientists call a nanosecond a "light foot," since light can travel approximately one foot in one nanosecond. You can also use this word figuratively, to mean "a really short length of time." Nano- comes from the Greek root nanos, "a dwarf."