Second (s) is the SI unit of time

The SI unit of time is the second, symbolized by s. It forms the foundation for measuring time intervals in science. This tiny unit is based on the incredibly precise vibrations of a caesium atom. Many other familiar units, like minutes (min), hours (h), and days (d), are derived from or related to seconds. For instance, there are 60 seconds in a minute and 3600 seconds in an hour.

One second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.