A constant is a number with a known, fixed value. Examples of constants include regular numbers written with digits, like $15,$ $\text{-}\frac{2}{3},$ and $11.327.$ When a constant appears as an addend in an algebraic expression, the constant is referred to as a constant term.

Certain constants occur often enough to be given their own symbols — one such constant is pi, which is represented by the Greek letter $\pi .$