This is what I find in
The phrase "display" is usually used to refer to a collection of monitors that share a common set of input devices (keyboard, mouse, tablet, etc.). Most workstations tend to only have one display. Larger, multi-user systems, however, frequently have several displays so that more than one person can be doing graphics work at once. To avoid confusion, each display on a machine is assigned a display number (beginning at 0) when the X server for that display is started. The display number must always be given in a display name.
My question is: Do we need to start multiple X servers if we want to use multiple displays, or all those displays can be handled by a single X server? Is it possible to share keyboards, mice and monitors across different displays?
Edit. The display here refers to the concept defined by the X window system, not a single monitor. I know there are Xinerama and XRandR technologies that support multi-head configurations.