WordPress at a glance
action is not described

admin_action_(action) action-hook . WP 2.6.0

Fires when an 'action' request variable is sent.

The dynamic portion of the hook name, $_REQUEST['action'], refers to the action derived from the GET or POST request.

Usage

add_action( 'admin_action_(action)', 'action_function_name_5481' );
function action_function_name_5481(){
	// action...
}

Where the hook is called

In file: /wp-admin/admin.php
admin_action_(action)
wp-admin/admin.php 362
do_action( 'admin_action_' . $_REQUEST['action'] );

Where the hook is used (in WP core)

Does not used.