The contents of /etc/motd are displayed by login(1) after a successful login but just before it executes the login shell.
The abbreviation "motd" stands for "message of the day", and this file has been traditionally used for exactly that (it requires much less disk space than mail to all users).
This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
cdist-type__motd(7), gsisshd(8), issue(5), pam_motd(8), sshd(8).