An X terminal is an electronic display terminal that communicates with a host computer system using the X Window protocol developed at the Massachusetts Institute of Technology.
The X Window protocol allows a program running on the host computer system to display both formatted text and graphics on the X terminal. Since the X Window protocol is defined to work over any TCP/IP network, X terminals connected to the Internet can be connected to hosts located anywhere on the Internet.
Personal computers (including both PCs and Macintoshes) can execute programs, usually called X servers, that make them act like X Window terminals and are frequently used as X terminals.