(plural loci), 1715, "locality," from Latin locus "a place, spot, position," from Old Latin stlocus, literally "where something is placed," from PIE root *st(h)el- "to cause to stand, to place." Used by Latin writers for Greek topos. Mathematical sense by 1750.
locus lo·cus (lō'kəs)
n. pl. lo·ci (-sī', -kē, -kī')
A place; site.
The position that a given gene occupies on a chromosome.
plur. loci (loh-seye, loh-keye)
In geometry, the set of all points (and only those points) that satisfy certain conditions; these points form a curve or figure. For example, the locus of all points in space one foot from a given point is a sphere having a radius of one foot and having its center at the given point. The locus of all points in a plane one foot from a given point is a circle having a radius of one foot and having its center at the given point.