A black hat is often a term to describe a villain or bad guy, this metaphor is visualized in western movies where the 'baddie' wears a black hat in contrast to the hero's white hat. The phrase is used in computing slang, where it refers to a hackers or the 'dark arts' of search engine optimization (also called spamdexing). Using black hat tricks in optimization of sites will result in being banned by the major search engine. Over loading keywords, meta tags and content key words will result in a loss of ranking and will inevitably lead to your website un-indexed.
Black hat applied in the Search Engine Optimization (SEO) industry, uses SEO tactics that attempt to redirect search results to particular target pages in a fashion that is against the search engines' terms of service. White hat methods are generally approved by the search engines.
Some of the blackhat SEO tactics include: keyword stuffing, hidden text and links, doorway and cloaked pages, link farming and blog comment spam.
Getting off a blacklist is difficult and can be a frustrating experience - Don't black Hat!