constant

A constant is a quantity that does not vary. In mathematics, a constant is a fixed number that does not depend on a variable; expressions may contain constants such as 5 or π. By contrast, a variable can change as other quantities change.

Mathematical constants are numbers with fixed, universal values within mathematics. Common examples include π, the ratio of a circle’s circumference to its diameter; e, the base of natural logarithms; and φ, the golden ratio. Some constants are algebraic (such as √2) and others are transcendental (such as π and e). These constants often appear as limits, coefficients, or values in formulas and theorems, and many are dimensionless.

In physics, physical constants are quantities believed invariant in nature and used to express laws of nature, such as the speed of light in vacuum c, the Planck constant h, the elementary charge e, Boltzmann’s constant kB, and Newton’s gravitational constant G. Some constants are considered fundamental, while others are defined or derived within particular theories. The values of dimensional constants can depend on the units chosen, while dimensionless constants are independent of those choices.

In computing, a constant (or constant value) is a value that remains unchanged after it is defined, contrasting with variables whose contents can be modified during program execution.

The term constant comes from Latin constans, meaning steadfast. Constants play central roles across mathematics, science, and programming, serving as fixed references that anchor formulas, measurements, and algorithms.