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 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.