The time taken for light to travel a specified distance in a vacuum, usually one centimetre, but sometimes one foot or the width of a nucleon.
A very short, unspecified length of time.
A unit of time defined by the frequency of its basic timer – historically, and by convention, 0.01 of a second, but some computer operating systems use other values.
The length of an alternating current power cycle (1/60 or 1/50 of a second).