Rectangular, or Cartesian, coordinates indicate a location on a graph that has two perpendicular axes. In this system, x is the horizontal axis, y is the vertical axis and point (x,y) is the rectangular coordinate for a point on the graph.
Rene Descartes invented the Cartesian, or rectangular, coordinate system in the 17th century. In contrast, polar coordinates express the location on the graph in terms of a distance, r, from the origin point (0.0), which is where the x and y axes cross, and an angle measurement from the x-axis. According to the Pythagorean theorem, the distance from the origin of a Cartesian point (x,y) is the square root of the sum of x squared and y squared.