XDM
XDM stands for X Display Manager, a graphical login manager for the X Window System. It is responsible for presenting a login prompt, starting the X server, and launching a user session. XDM was part of early X11 distributions and remains available as a simple, lightweight display manager in many Unix-like systems, though it has largely been superseded by more feature-rich alternatives such as GDM and LightDM.
XDM supports XDMCP (X Display Manager Control Protocol) for initiating sessions from remote hosts, enabling remote
Configuration for XDM is handled via a small set of files, typically located under /etc/X11/xdm, including Xservers
Other uses: The acronym XDM is also used by other software projects, notably Xtreme Download Manager, a