efaq: File-name conventions
1.4 What are ‘src/config.h’, ‘site-lisp/default.el’, etc.?
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These are files that come with Emacs. The Emacs distribution is divided
into subdirectories; e.g., ‘etc’, ‘lisp’, and ‘src’. Some of these
(e.g., ‘etc’ and ‘lisp’) are present both in an installed Emacs and in
the sources, but some (e.g., ‘src’) are only found in the sources.
If you use Emacs, but don’t know where it is kept on your system,
start Emacs, then type ‘C-h v data-directory <RET>’. The directory name
displayed by this will be the full pathname of the installed ‘etc’
directory. (This full path is recorded in the Emacs variable
‘data-directory’, and ‘C-h v’ displays the value and the documentation
of a variable.)
The location of your Info directory (i.e., where Info documentation
is stored) is kept in the variable ‘Info-default-directory-list’. Use
‘C-h v Info-default-directory-list <RET>’ to see the value of this
variable, which will be a list of directory names. The last directory
in that list is probably where most Info files are stored. By default,
Emacs Info documentation is placed in ‘/usr/local/share/info’.
For information on some of the files in the ‘etc’ directory, 
Informational files for Emacs.
Info Catalog
efaq: Emacs manual
efaq: FAQ notation
efaq: Common acronyms