WordPress at a glance
action is not described

delete_(meta_type)_meta action-hook . WP 3.1.0

Fires immediately before deleting metadata of a specific type.

The dynamic portion of the hook, $meta_type, refers to the meta object type (comment, post, term, or user).

Usage

add_action( 'delete_(meta_type)_meta', 'action_function_name_94', 10, 4 );
function action_function_name_94( $meta_ids, $object_id, $meta_key, $meta_value ){
	// action...
}
$meta_ids(array)
An array of metadata entry IDs to delete.
$object_id(int)
Object ID.
$meta_key(string)
Meta key.
$meta_value(mixed)
Meta value.

Where the hook is called

delete_metadata()
delete_metadata_by_mid()
wp-includes/meta.php 391
do_action( "delete_{$meta_type}_meta", $meta_ids, $object_id, $meta_key, $_meta_value );
wp-includes/meta.php 786
do_action( "delete_{$meta_type}_meta", (array) $meta_id, $object_id, $meta->meta_key, $meta->meta_value );

Where the hook is used (in WP core)

Does not used.