Xterm
In computing, xterm is the standard terminal emulator for the X Window System. It allows users to run programs which require a command-line interface. If no particular program is specified, xterm runs the user's shell. An X display can show one or more user's xterm windows output at the same time. Each xterm window is a separate process, but all share the same keyboard, taking turns as each xterm process acquires "focus". Normally focus switches between X applications as the user moves the pointer (e.g., a mouse cursor) about the screen, but xterm provides options to  grab focus (the "Secure Keyboard" feature) as well as accept input events sent without using the keyboard (the "Allow SendEvents" feature). Those options have limitations, as discussed in the xterm manual. xterm originated prior to the X Window System. It was originally written as a stand-alone terminal emulator for the VAXStation 100 (VS100) by Mark Vandevoorde, a student of Jim Gettys, in the summer of 1984, when work on X started. It rapidly became clear that it would be more useful as part of X than as a standalone program, so it was retargeted to X. As Gettys tells  the story, "part of why xterm's internals are so horrifying is that it was originally intended that a single process be able to drive multiple VS100 displays." After many years as part of the X reference implementation, around 1996 the main line of development then shifted to XFree86 (which itself forked from X11R6.3), and it is now maintained by Thomas Dickey. Many xterm variants are also available. Most terminal emulators for X started as variations on xterm. Features. Terminal emulation. Early versions emulated the VT102 and Tektronix 4014. Later versions added control sequences for DEC and other terminals such  as: Customization. As with most X applications, xterm can be customized via global X resources files (e.g. /usr/lib/X11/app-defaults/XTerm), per-user resource files (e.g. ~/XTerm, ~/.Xresources), or command-line arguments. Most of the command-line options correspond to resource settings, as noted in the manual page. While the name of the program is "xterm", the X resource class is "XTerm". The uxterm script overrides this, using the "UXTerm" resource class. xterm normally does not have a menu bar. To access xterm's three menus, users hold the control key and press the left, middle, or right  mouse button. Support for a "toolbar" can be compiled-in, which invokes the same menus. Protocols. Supported terminal control functions include: In addition to protocols used in commercially available terminal machines, xterm added a few protocols that have been adopted by other terminal emulators, such as: