SECOND

The second is the SI base unit of time, symbol s. It defines a duration that is convenient for science and everyday life and provides the standard by which clocks, experiments, and communication systems are synchronized worldwide.

Historically, the second was once defined as 1/86400 of a mean solar day. Since 1967 it has been defined by the frequency of radiation from the cesium-133 atom: 9,192,631,770 periods corresponding to the transition between two hyperfine states.

A minute equals 60 seconds and an hour equals 3,600 seconds. The second is used for timing across laboratories, manufacturing, navigation, and sports, and is the basis for timekeeping systems such as Coordinated Universal Time (UTC).

As an ordinal, second denotes the position following the first. The term, from Latin secundus via Old French, also appears in phrases such as second-in-command, second-best, and second-place.

In music, a second is the interval between two adjacent pitches (major or minor). In geometry, an arcsecond is 1/3600 of a degree. Colloquially, "in a second" means very soon.