Lo·cus n.; pl. Loci & Loca
 1. A place; a locality.
 2. Math. The line traced by a point which varies its position according to some determinate law; the surface described by a point or line that moves according to a given law.
 Plane locus, a locus that is a straight line, or a circle.
 Solid locus, a locus that is one of the conic sections.

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