What is the difference between screenX/Y, clientX/Y and pageX/Y?

Question

What is the difference between screenX/Y, clientX/Y and pageX/Y?

Also for iPad Safari,

Answer 1

clientX/Y refers to relative screen coordinates, for instance if your web-page is long enough then clientX/Y gives clicked point's coordinates location in terms of its actual pixel position while ScreenX/Y gives the ordinates in reference to start of page.