White hat SEO – It is the most popular SEO technique that utilizes methods and techniques to improve search engine rankings of a site which do not run afoul of search engine guidelines. White hat SEO uses techniques like high quality content, link acquisition, website HTML optimization, and restructuring. With White hat SEO, you can expect a long lasting growth in your rankings.
Black hat SEO – It exploits the various weaknesses in the search engines algorithms to get high rankings. The Black hat SEO is not in accordance with the SEO guidelines set by search engines. Some of the black hat SEO techniques are keyword stuffing, link spam, hidden text, hidden link. Using these techniques, you can expect unpredictable, quick but short lasting growth in rankings.
Grey hat SEO – Grey hat SEO is neither black nor white, it rather combines both. It is a transformation from black SEO techniques to white SEO techniques and from white SEO techniques to black SEO techniques.