A locus is a set of points that share a certain property. For example, a circle with center O and radius r consists of all the points whose distance from the center of the circle is equal to the circle's radius and no other points. This makes the circle the locus of points for which the distance from O is equal to r. In this example, the property shared by every point in the locus is the distance from the point O is equal to r. Many examples of loci appear in plane geometry.