White Hat SEO refers to the usage of optimization strategies, techniques and tactics that focus on a human audience opposed to search engines and completely follows search engine rules and policies.

    Black Hat SEO refers to the use of aggressive SEO strategies, techniques and tactics that focus only on search engines and not a human audience, and usually does not obey search engines guidelines.

    Gray Hat SEO is the practice of using technically legal methods to improve your site rankings, but which are ethically dubious, and could one day become black hat.