Unit of time

A unit of time or midst unit is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI) and by extension most of the Western world, is the second, defined as about 9 billion oscillations of the caesium atom.
Note: The light-year is not a unit of time, but a unit of length of about 9.5 petametres (9 454 254 955 488 kilometers).