Lo"cus (?), n.; pl. Loci (#), & Loca (#). [L., place. Cf. Allow, Couch, Lieu, Local.]
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.
© Webster 1913.