Definition:Distance/Points/Real Numbers

Definition
Let $x, y \in \R$ be real numbers.

Let $\size {x - y}$ be the absolute value of $x - y$.

Then the function $d: \R^2 \to \R$:
 * $\map d {x, y} = \size {x - y}$

is called the distance between $x$ and $y$.

Also see

 * Distance on Real Numbers is Metric