Measurement of time is built on units, such as:
Unit of time are used to:
- define an instant. The more unit, the more precision
- define an amount of time (ie duration or period) when every unit has a quantity (2 year, …)
Second is the base unit of time in the International System of Units (SI), see Time - Second
The units of time are also known as the datetime fields because they make up a date time value.