eintr: Site-wide Init
16.1 Site-wide Initialization Files
===================================
In addition to your personal initialization file, Emacs automatically
loads various site-wide initialization files, if they exist. These have
the same form as your ‘.emacs’ file, but are loaded by everyone.
Two site-wide initialization files, ‘site-load.el’ and
‘site-init.el’, are loaded into Emacs and then dumped if a dumped
version of Emacs is created, as is most common. (Dumped copies of Emacs
load more quickly. However, once a file is loaded and dumped, a change
to it does not lead to a change in Emacs unless you load it yourself or
re-dump Emacs. 
Building Emacs (elisp)Building Emacs, and the
‘INSTALL’ file.)
Three other site-wide initialization files are loaded automatically
each time you start Emacs, if they exist. These are ‘site-start.el’,
which is loaded _before_ your ‘.emacs’ file, and ‘default.el’, and the
terminal type file, which are both loaded _after_ your ‘.emacs’ file.
Settings and definitions in your ‘.emacs’ file will overwrite
conflicting settings and definitions in a ‘site-start.el’ file, if it
exists; but the settings and definitions in a ‘default.el’ or terminal
type file will overwrite those in your ‘.emacs’ file. (You can prevent
interference from a terminal type file by setting ‘term-file-prefix’ to
‘nil’. A Simple Extension Simple Extension.)
The ‘INSTALL’ file that comes in the distribution contains
descriptions of the ‘site-init.el’ and ‘site-load.el’ files.
The ‘loadup.el’, ‘startup.el’, and ‘loaddefs.el’ files control
loading. These files are in the ‘lisp’ directory of the Emacs
distribution and are worth perusing.
The ‘loaddefs.el’ file contains a good many suggestions as to what to
put into your own ‘.emacs’ file, or into a site-wide initialization
file.
Info Catalog
eintr: Default Configuration
eintr: Emacs Initialization
eintr: defcustom