These term labels techniques to improve your site’s search engine exposure into two categories:
Black Hat SEO Techniques are those that Search Engines don’t approve of.
This are typically schemes or strategies that trick the search engine into thinking your website warrants more exposure than it otherwise should.
White Hat refers to SEO techniques that search engines sanction.
The labels relates to old Westerns movies where the bad guy wore a black hat, and of course the good guys wore White Hats.