locus (loci)

A locus is a line, a curve or a region of points that satisfies a specific rule.

We can use a circle as an example of a locus.

This circle is the locus of points that are 2 cm from point A. Its centre is A and its radius is 2 cm.

Therefore, the locus of points that are less than 2 cm from A is the region inside the circle, and the locus of points that are greater than 2 cm from A is the region outside the circle.