Coordinate Axes and Coordinate Planes in Three Dimensional Space
Consider three planes intersecting at a point O such that these three planes are mutually perpendicular to each other. These three planes intersect along the lines X, Y & Z, called the x, y and z-axes, respectively. We may note that these lines are mutually perpendicular to each other. These lines constitute the rectangular coordinate system. The planes XOY, YOZ and ZOX, called, respectively the XY-plane, YZ-plane and the ZXplane, are known as the three coordinate planes. The point O is called the origin of the coordinate system. The three coordinate planes. These three coordinate planes divide the space into eight parts known as octants.
Note: By convention, we take the XOY plane as the plane of the paper and the line Z ′ OZ as perpendicular to the plane XOY.