Black hat SEO refers to techniques and strategies used to get higher search rankings, and breaking search engine rules. Black hat SEO focuses on only search engines and not so much a human audience. ... White hat SEO refers to the use of techniques and strategies that target a human audience opposed to a search engine.
Black hat SEO:-Techniques utilized by the seo specialists that is unauthorized,unethical and do not approved by the search engines.Site is eventually prohibited by the computer program if it's caught.
White hat seo:-They use the correct and real techniques that are accepted by the search engines and it does not damage the web site.
Grey hat seo:-They use the technically correct techniques for promoting their sites.