By definition, a locus of points is: a curve or other figure formed by all the points satisfying a particular equation of the relation between coordinates. The plural of locus is loci.
Some loci are simple, like a circle. Others are rather complicated. We will look at familiar loci from the conic sections. We will also look at loci that will remind you of your experiments with the Spirograph toy. How about a four bar linkage for the engineers? That will generate a locus of points. Would you believe that a small portion of a train is actually moving backwards? We’ll investigate this and all the loci using an open source dynamic geometry program called Geogebra.