Techopedia explains
Black Hat Search Engine Optimization (Black Hat SEO)
Examples of black hat SEO methods include:
- Keyword Stuffing: Loading extensive keyword lists into alt tags, metatags, and comment tags in text that is invisible to human eyes. This repeated flooding of exactly the same keywords within a Web page is designed to trick search engine algorithms, which read the keywords and rank the Web page high in their search results.
- Link Building/Farming: Posting a website URL to a site that consists of a link directory with many links to other websites with completely unrelated content.
- Doorway Pages: These pages are indexed by the search result. However, when users enter a doorway page, they are redirected to an unrelated Web page.
- Invisible/Hidden Text: Inserting long lists of white-text keywords into a white background. This technique is considered spam, which can cause search engines to ban those who use it.
The definition of black hat SEO is meaningful in contrast to white hat SEO. Search engines are geared toward directing users to websites that most appropriately match their queries. Metadata, tags, headers, inbound links and other data factor into search engine results and hierarchies. White hat SEO focuses on strengthening data point accuracy to fully reflect Web page search content results. Black hat SEO techniques are used in an attempt to trick search engines into directing users to a page that appears to answer or match user search queries, but may in fact contain unrelated content.
Search engines algorithms have adjusted to nullify basic black hat SEO techniques such as keyword stuffing. In certain extreme cases, search engines may lower the offending page's rank or delete the offender from search results.