The document describes the Cartesian coordinate system, which uses perpendicular x and y axes that intersect at the origin (0,0) to locate and plot points on a plane. The x-axis divides the plane into positive and negative numbers, and likewise for the y-axis, creating four quadrants. Ordered pairs (x,y) are used to specify points, with the x-value being the abscissa and y-value being the ordinate.