ABSTRACT
A locus (plural loci ) is the path traced out by a point that moves under given definite conditions.
You may not have been aware of it, but you have met loci many times before. One of the most common loci is that of a point that moves so that its distance from another fixed point remains constant: this produces a circle. Another locus that you know is that of a point that moves so that its distance from a line remains constant: this produces parallel lines.
