Unethical techniques used to artificially inflate search engine optimiztion, e.g. invisible text (black text keywords on black background; cannot be seen by human eye, but detected by bots), keyword stuffing (repetitive use of keywords on page), and doorway pages (highly optimized pages that redirect user to a different site). These and other Black-Hat SEO procedures are to be avoided, for if detected by search engines, can lead to expulsion from indices.