X is the abscissa, Y is the ordinate of a point in a plane rectangular coordinate system, and the vertical lines from point P to X axis and Y are M and N respectively. At this time, the number corresponding to point M on X axis is called the abscissa of point P, and the number corresponding to point N on Y axis is called the ordinate of point P. Combined with the knowledge of ordered number pairs, we call the number pair composed of two numbers A and B in sequence an ordered number pair.