**is a common term for the**

*The Metric System***International System of Units**.

In mathematics, a **metric** (also called **distance metric**) is an abstraction of the notion of *distance*; it is used to define metric spaces. The article on metric spaces contains a detailed discussion of the topic.

An important special case is the metric that turns a manifold into a Riemannian manifold. Such a metric allows to introduce geodesics and to measure distances and angles on the manifold.