get_subdirectory_reserved_names()

function get_subdirectory_reserved_names() {
	$names = array(
		'page', 'comments', 'blog', 'files', 'feed', 'wp-admin',
		'wp-content', 'wp-includes', 'wp-json', 'embed'
	);

	/**
	 * Filters reserved site names on a sub-directory Multisite installation.
	 *
	 * @since WP-3.0.0
	 * @since WP-4.4.0 'wp-admin', 'wp-content', 'wp-includes', 'wp-json', and 'embed' were added
	 *              to the reserved names list.
	 *
	 * @param array $subdirectory_reserved_names Array of reserved names.
	 */
	return apply_filters( 'subdirectory_reserved_names', $names );
}