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