Black hat is a common term known to search engine optimisers, it is considered as unethical techniques used to get websites increased exposure in search engines.
Search engines such as Google, Yahoo! and MSN wants to ensure they are showing relevant results to their end users. For those who employ successful ?Black hat? or ?Unethical? techniques to get their sites to show up in the search results pages, more often than not, will not give you the information you were looking for.