In mathematics, the unit is a standard used to measure or express quantity. It can be a standard quantity to compare the sizes of other similar quantities. Units are usually used to describe physical quantities such as length, mass, time, temperature and speed.

Units can be divided into basic units and derivative units. Basic units are independent and inseparable units, such as meters, kilograms, seconds, etc. Derived units are units based on the combination of basic units, such as square meters, kilograms/cubic meters, etc.

In mathematics, the use of units can help us to quantify and measure various physical and mathematical concepts, so as to accurately calculate, compare and analyze them. The selection and use of units should conform to the international system of units (SI system) commonly used in the world or the system of units in other specific fields.

To sum up, the unit is a standard used in mathematics to express and measure quantities, which is helpful for accurate calculation and comparison.