# Constant

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A **constant** is a variable that does not change, it has a final value.

Constants are defined in the `const`

section of a Free Pascal program. When a symbol is defined as constant, the Free Pascal compiler can often do some optimizations to make the output code faster or smaller.

Some special Free Pascal constants are:

Logical truth values

data type limits

The mathematical value π is realized as a function in `System.Pi`

, so you may shadow (redefine) it on your own.