second

Basic SI unit of time, one-sixtieth of a minute. It is defined as the duration of 9,192,631,770 cycles of regulation (periods of the radiation corresponding to the transition between two hyperfine levels of the ground state) of the caesium-133 isotope. In mathematics, the second is a unit (symbol ") of angular measurement, equalling one-sixtieth of a minute, which in turn is one-sixtieth of a degree.