|Original author(s)||Mark Vandevoorde|
371  / 24 February 2022
|Operating system||Unix, Unix-like, MVS OpenVMS, OS/2|
|License||MIT/X Consortium License|
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.
Early versions emulated the VT102 and Tektronix 4014. 
Later versions added control sequences for DEC and other terminals such as:
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.
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:
Initially Xterm supported only Portable Compiled Format (PCF) bitmap font until 2000 when Xft library was introduced to support modern stroke-based fonts like TrueType. 
The X Window System is a windowing system for bitmap displays, common on Unix-like operating systems.
A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.
ANSI escape sequences are a standard for in-band signaling to control cursor location, color, font styling, and other options on video text terminals and terminal emulators. Certain sequences of bytes, most starting with an ASCII escape character and a bracket character, are embedded into text. The terminal interprets these sequences as commands, rather than text to display verbatim.
A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and predated the use of a computer screen by decades.
Cygwin/X is an implementation of the X Window System that runs under Microsoft Windows. It is part of the Cygwin project, and is installed using Cygwin's standard setup system. Cygwin/X is free software, licensed under the X11 License.
In computing, text-based user interfaces (TUI), is a retronym describing a type of user interface (UI) common as an early form of human–computer interaction, before the advent of modern conventional graphical user interfaces (GUIs). Like GUIs, they may use the entire screen area and accept mouse and other inputs. They may also use color and often structure the display using special graphical characters such as ┌ and ╣, referred to in Unicode as the "box drawing" set. The modern context of use is usually a terminal emulator.
X.Org Server is the free and open-source implementation of the X Window System display server stewarded by the X.Org Foundation.
PuTTY is a free and open-source terminal emulator, serial console and network file transfer application. It supports several network protocols, including SCP, SSH, Telnet, rlogin, and raw socket connection. It can also connect to a serial port. The name "PuTTY" has no official meaning.
Rxvt is a terminal emulator for the X Window System, and in the form of a Cygwin port, for Windows.
GNU Midnight Commander is a free cross-platform orthodox file manager. It was started by Miguel de Icaza in 1994 as a clone of the then-popular Norton Commander.
The Tektronix 4010 series was a family of text-and-graphics computer terminals based on storage-tube technology created by Tektronix. Several members of the family were introduced during the 1970s, the best known being the 11-inch 4010 and 19-inch 4014, along with the less popular 25-inch 4016. They were widely used in the computer-aided design market in the 1970s and early 1980s.
GNOME Terminal is a terminal emulator for the GNOME desktop environment written by Havoc Pennington and others. Terminal emulators allow users to access a UNIX shell while remaining on their graphical desktop.
A multiseat, multi-station or multiterminal system is a single computer which supports multiple independent local users at the same time.
NCSA Telnet is an implementation of the Telnet protocol created at the National Center for Supercomputing Applications of the University of Illinois at Urbana-Champaign. It was first released in 1986 and continuously developed until 1995. The initial implementation ran under Mac OS and Microsoft MS-DOS and provided basic DEC VT102 terminal emulation as well as support for multiple simultaneous connections and an internal FTP server. At the time, NCSA Telnet was the first implementation of telnet for the Macintosh or a PC that provided the ability to connect to multiple hosts simultaneously.
AbsoluteTelnet is a software terminal client for Windows that implements Telnet, SSH 1 and 2, SFTP, TAPI Dialup and direct COM port connections. It is commercial software, originally released in 1999 and is still in regular development by Brian Pence of Celestial Software.
ZOC is a popular computer-based terminal emulator and Telnet software client for the Microsoft Windows and Apple Macintosh macOS operating systems that supports telnet, modem, SSH 1 and 2, ISDN, serial, TAPI, Rlogin and other means of communication. Its terminal emulator supports Xterm emulation with full colors, meta-keys and local printing, VT102, VT220 and several types of ANSI as well as Wyse, TVI, TN3270, and Sun's CDE. It supports full keyboard remapping, scripting in REXX and other languages, and support for named pipes.
SecureCRT is a commercial SSH and Telnet client and terminal emulator by VanDyke Software. Originally a Windows product, VanDyke later added a Mac OS X version in 2010 with release v6.6 and a Linux version in 2011 with release v6.7.
A terminal multiplexer is a software application that can be used to multiplex several separate pseudoterminal-based login sessions inside a single terminal display, terminal emulator window, PC/workstation system console, or remote login session, or to detach and reattach sessions from a terminal. It is useful for dealing with multiple programs from a command line interface, and for separating programs from the session of the Unix shell that started the program, particularly so a remote process continues running even when the user is disconnected.
The VT320 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1987. The VT320 is the text-only version, while the VT330 adds monochrome ReGIS, Sixel and Tektronix 4010 graphics, and the VT340 adds color.
Bracketed paste, is a mode of some terminal emulators which allows programs running in the terminal to treat pasted text differently from text typed normally.