WordPress at a glance
action is not described

mature_blog action-hook . WP 3.1.0

Fires when the 'mature' status is added to a site.

Usage

add_action( 'mature_blog', 'action_function_name_6360' );
function action_function_name_6360( $site_id ){
	// action...
}
$site_id(int)
Site ID.

Where the hook is called

wp_maybe_transition_site_statuses_on_update()
mature_blog
wp-includes/ms-site.php 1181
do_action( 'mature_blog', $site_id );

Where the hook is used (in WP core)

Does not used.