If a point moves in such a way that it satisfies some given geometric conditions at each instant during its motion, then the path traced out by the moving point is called its locus.
A point that does not satisfy the given geometrical condition (or conditions) cannot lie on the locus.
The Locus of a point equidistant from a fixed point is a circle with a fixed point as the center.
The locus of a point, equidistant from two given points, is the perpendicular bisector of the line segment joining the two points