\begin{definition}[Definition:Metric Space/Triangle Inequality]
Let $M = \struct {A, d}$ be a metric space, satisfying the metric space axioms:
{{:Axiom:Metric Space Axioms}}
Axiom $\text M 2$ is referred to as the '''triangle inequality''', as it is a generalization of the Triangle Inequality which holds on the real number line and complex plane.
\end{definition}