# Constant

## Definition

A **constant** is a number with fixed value, unlike a variable that can change or that is used to represent an unknown value.

The word constant is also used in other contexts or as part of other expressions:

### Constant function

A constant function is a function which has a constant output: the value of the function does not depend on the value of its input. Equivalently, a constant function is a function whose range has only a single value.

### Constant term of a polynomial

The **constant term** of a polynomial in variables is the coefficient of . In the case of a polynomial in a single variable , it is the coefficient of the term . Normally, when we write out a polynomial, the constant term is the term with no variables present, e.g. for the polynomial , the constant term is .

Note that in general, the constant term of a polynomial is simply the value .

## Examples

, or pi is a famous constant that is approximately 3.14159.

, or e is another famous constant that is approximately 2.71828.

All numbers are constants because they do not change their value; they always remain the same.