widgets_init action-hook . WP 2.2.0

Fires after all default WordPress widgets have been registered.

Usage

add_action( 'widgets_init', 'action_function_name_3250' );
function action_function_name_3250(){
	// action...
}

Where the hook is called

do_action( 'widgets_init' );

Where the hook is used (in WP core)

add_action( 'widgets_init', array( $this, 'register_settings' ), 95 );

add_action( 'widgets_init', array( $this, '_register_widgets' ), 100 );