What is the X in X-mas?
1640s, "of the same order," from Medieval Latin coordinatus, past participle of coordinare "to set in order, arrange" (see coordination). Meaning "involving coordination" is from 1769. Related: Coordinance.
1823, in the mathematical sense, especially with reference to the system invented by Descartes; from coordinate (adj.). Hence, coordinates as a means of determining a location on the earth's surface (especially for aircraft), attested by 1960.
1660s, "to place in the same rank," from Latin coordinare (see coordination). Meaning "to arrange in proper position" (transitive) is from 1847; that of "to work together in order" (intransitive) is from 1863. Related: Coordinated; coordinating.
A set of numbers, or a single number, that locates a point on a line, on a plane, or in space. If the point is known to be on a given line, only one number is needed to locate it. If the point is known to be on a given plane, two numbers are needed. If the point is known to be located in space, three numbers are needed.