grid - a 3D grid system, named for the French philosopher Descartes, who defined the underlying idea of a 2D grid. The 2D grid (using x- and y-axes) is commonly used in algebra and geometry to map lines derived from equations and to deal with geometric shapes. The 3D grid required the addition of a third axis, running through the 0,0 point -- the x-y intersection -- and being perpendicular to both existing axes. With the addition of the third axis, any point in space can be defined by x-, y-, and z-coordinates (positive or negative), provided that one knows where the 0,0,0 point is and what the orientation of the grid is. In CAD systems, the grid system is a given, and all object are oriented within the grid. (Positive x is normally assumed to be east, positive y to be north, and positive z to be up.)