Event coordinates and element dimentions on a page

Event coordinates

Diagram showing the properties relative to the mouse event.

Element coordinates

Diagram showing the properties of a element with respect to its parent. The one with the green outline is the parent and the one with the red outline is the child. In this case, the child is larger than the parent and overflows out of it in both x and y directions.
There are several more but most of the time, the ones you see here will be sufficient.