The path traced out by a moving point, which can be defined
as the set of all points on a curve satisfying given conditions.
The locus of points a fixed distance from a fixed point is
a circle. The locus of a point equidistant from two fixed
points is a straight line that perpendicularly bisects the
line joining them. The locus of points a fixed distance from
a line is two parallel lines running either side.
the locus of points which are the same distance from
two fixed points A and B is the red line in the diagram. It
is the perpendicular bisector of AB.