it's the methods that Google doesn't want you to use. Now slow down on the dictionary questions and learn how to use the forum search function.
Black hat SEO is really based around the idea of using a relatively 'no holds barred' approve to getting to where you want - be that rankings/traffic etc... without worrying if it is against the search engines (ie. Google!) terms and conditions. There are lots of opinions on it's ethicalness, from people saying things like 'Who made Google in charge, why should we follow their draconian rules???!' To people saying 'It's best to be ethical, white hat etc, why do bad business and try to trick people, it's immoral' Which ever school of though you belong to, it is usually fair to say this next sentence is true: 'If Google catch you doing black hat SEO, they will penalise or ban you.' In my opinion? - Stick to white hat - act in the online world as you would in the offline world - don't try to trick and cheat your way to success, and be prepared to stand behind anything you do in the online business world, just as you should in the offline business world. --- But that's just my ethos! [edit] - Oh, and as I ashamedly don't yet have an SEO glossary on my own site, here is a link to one on a site that's pretty trustworthy and spot on: http://www.seobook.com/glossary/#black-hat-seo I agree with the person above though, you should also use this: http://forums.digitalpoint.com/search.php !!!
Are you referring to black hat SEO? It uses unethical ways in order to get back links. Door-way page, cloaking, link farms, keyword stuffing and invisible text are just some of the methods that falls under black hat.
here's the section of wikipedia article that describes whitehat and blackhat seo http://en.wikipedia.org/wiki/Search_engine_optimization#White_hat_versus_black_hat