WordPress at a glance
action is not described

muplugins_loaded action-hook . WP 2.8.0

Fires once all must-use and network-activated plugins have loaded.

Usage

add_action( 'muplugins_loaded', 'action_function_name_6960' );
function action_function_name_6960(){
	// action...
}

Where the hook is called

In file: /wp-settings.php
muplugins_loaded
wp-settings.php 295
do_action( 'muplugins_loaded' );

Where the hook is used (in WP core)

Does not used.