Definition:Bound Variable

Definition
A dummy variable (or bound variable) is a variable which, when it occurs in an expression, can be replaced with another variable without changing the meaning of the statement.

Examples
See the definition of universal statement.

In the statement:
 * $\forall x: P \left({x}\right)$

the variable $x$ is a dummy variable.

Also see the definition of existential statement.

In algebra:
 * $x^2 + 2 x y + y^2 = \left({x + y}\right)^2$

Both $x$ and $y$ are dummy variables.

Also known as
In treatments of pure logic, this is sometimes known as an individual variable.