This is a method to get top the SERP with your keywords by using illegal ways. By using these techniques you can be banned by Google. In other words Black hat SEO is unethical way of site promotion. In this method the keywords are hidden on the home page. These websites are usually caught and removed from the search engines.
To use unapproved methods to get quick inclusion in SERP, is called Black Hat seo. Normally google likes human effort. If you do a big amount of work through your software such as blog commenting and link building or hidden activities on your page (which user does not see), come under black hat seo.
Black hat seo.....It is the technique against search engine guidelines....Black Hat SEO techniques include keyword stuffing, invisible text and doorway pages.
Agree with ^^ another reason is that Google makes people very angry by penalizing honest sites with things like their latest Panda update, this is very frustrating after a lot of hard work, no wonder there is a blackhat community.
The various illegal methods like hidden text, doorway pages etc that are used to promote the website is called black hat SEO.
As there is always an evil side of every valuable thing...So do SEO is. SEO People promising you for an instant results in days could be using these techniques. The results will be for short leaving. So what to do : If you are a client and can't take a chance with your money then go for a SEO Specialist with having his/her own website in top ten results in major search engines or having proven track records for clients with a long time period. Important.... Don't ask an SEO for Instant Result....! Only a client let its SEO person to think about Black Hat SEO. If you pay the right price and time to an SEO Expert then outcome will be like...wow!
Cloaking, hidden text, irrelevant keywords stuffing, and make bulk backlinks in less time, these all are black hat seo