Cartesian coordinates are an ordered set of real numbers that
defines the position of a point in terms of
its projection on to mutually perpendicular number
lines. In the plane, each point is defined
by two such projections, one on to the x-axis (the abscissa)
and one on to the y-axis (the ordinate),
and is written as an ordered pair of
real numbers (x, y). The same system works equally in spaces
of three or more dimensions.
Cartesian coordinates are the most common system of rectangular
coordinates employed in analytical
geometry. The term is named after René Descartes.