The 'X' term "display" refers to the image that is generated by an X server and displayed on one or several monitors. Each monitor view can be a separate xscreen, or the monitors can be sharing the task of showing an image that requires more than one monitor - the SLS case of the 'stretched desktop".

An X server can genrate only one display. Associated with that display is usually a mouse and keyboard for interacting with it.

It is possible to have two displays on a single computer, but it requires two X servers to be operating, and the second set of mouse/keyboard (if they are used).

Xi Graphics offers this feature as a special that was developed for a customer to use in Air Traffic Control systems.