What is the definition of a second?

Beginners

For a beginner, 'a second' is a term used to measure time. It is a very short amount of time and is equal to one sixtieth of a minute. It is the time it takes for something to happen quickly in a blink of an eye, like a lightning strike or a car honk.

Intermediate

'A second' is a unit of time equal to one sixtieth of a minute. It is also used to refer to the position or rank immediately after the first.

Advanced

In advanced contexts, a second can be 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 caesium-133 atom. This definition is used as the basis for international time standards.