org-modules is a variable defined in `org.el'.
Its value is

(org-w3m org-bbdb org-bibtex org-docview org-gnus org-info org-irc org-mhe org-rmail)

Modules that should always be loaded together with org.el.

If a description starts with , the file is not part of Emacs
and loading it will require that you have downloaded and properly
installed the Org mode distribution.

You can also use this system to load external packages (i.e. neither Org
core modules, nor modules from the CONTRIB directory). Just add symbols
to the end of the list. If the package is called org-xyz.el, then you need
to add the symbol `xyz', and the package must have a call to:

(provide 'org-xyz)

For export specific modules, see also `org-export-backends'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.