x, y coordinates are respectively the horizontal and vertical addresses of any pixel or addressable point on a computer display screen. The x coordinate is a given number of pixels along the horizontal axis of a display starting from the pixel (pixel 0) on the extreme left of the screen. The y coordinate is a given number of pixels along the vertical axis of a display starting from the pixel (pixel 0) at the top of the screen. Together, the x and y coordinates locate any specific pixel location on the screen. x and y coordinates can also be specified as values relative to any starting point on the screen or any subset of the screen such as an image. On the Web, each clickable area of an image map is specified as a pair of x and y coordinates relative to the upper left-hand corner of the image.