An X server is a server of connections to X terminals in a distributed network that uses the X Window System. From the terminal user's point-of-view, the X server may seem like a server of applications in multiple windows. Actually, the applications in the remote computer with the X server are making client requests for the services of a windows manager that runs in each terminal. X servers (as part of the X Window System) typically are installed in a UNIX-based operating system in a mainframe, minicomputer, or workstation.
The X server may be compared to Microsoft's Terminal Server product except that the latter is running on a Windows-based operating system. However, there are X servers designed to run on a Microsoft Windows-based operating system.