Constants and variables are a pair of categories that reflect the quantity of things in mathematics. Constant, also known as "constant", is a quantity that reflects the relative static state of things; Variables, also called "variables", are quantities that reflect the changing state of things. In practice, in order to study the regularity of movement and change of things or the quantitative relationship between things, people must abandon the specific content of things and abstract the concept of number from the regularity of things.

At first, this abstraction was realized by grasping the static process of the movement of things. This way of looking at things is reflected in mathematics, resulting in the concept of constant.