WordPress at a glance
action is not described

add_attachment action-hook . WP 2.0.0

Fires once an attachment has been added.

Usage

add_action( 'add_attachment', 'action_function_name_8585' );
function action_function_name_8585( $post_ID ){
	// action...
}
$post_ID(int)
Attachment ID.

Where the hook is called

wp_insert_post()
wp-includes/post.php 3694
do_action( 'add_attachment', $post_ID );

Where the hook is used (in WP core)

Does not used.