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.