screen-monitor-geometries returns the geometries of all the monitors of screen. A monitor corresponds to an entity that the host machine regards as a physical monitor.
screen-monitor-geometries ignores software manipulations like the desktop on GTK+.
The monitor geometry is a rectangle which includes all of its display area, including "system areas" like menubar and taskbar and so on. Examples of these include the Windows taskbar, the Mac OS X menu bar and the Mac OS X Dock.
screen-monitor-geometries differs from screen-internal-geometries by returning screen rectangles which include all the monitor areas, and also by ignoring desktop manipulations.
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015