Cartesian Coordinates -- from Wolfram MathWorld

Cartesian coordinates are rectilinear two- or three-dimensional coordinates (and therefore a special case of curvilinear coordinates) which are also called rectangular coordinates. The two axes of two-dimensional Cartesian coordinates, conventionally denoted the x- and y-axes (a notation due to Descartes), are chosen to be linear and mutually perpendicular. Typically, the x-axis is thought of as the "left and right" or horizontal axis while the y-axis is thought of as the...