White hat SEO is the ethical SEO. A white hat SEO plays as per the rules laid down by the search engines like Google and Bing. Search engines lay down rules as to how their services can be used by SEOs. Sometimes, the rules laid down by search engines regarding some aspects may not be very clear. These techniques are beneficial to both site visitors and search engines. White hat SEO improves search engine results in such a way that search engines don’t punish the site like blocking your site from their search results. But, white hat SEO gives results slower than the black that SEO and is an ongoing process. Examples of white hat SEO techniques are: creating quality content, site optimization, guest blogging, internal linking, semantic mark-up, link baiting, etc.
Black hat SEO is the unethical form of SEO. It refers to the use of techniques which are not acceptable to search engines to improve the rankings of the site. These techniques aim to fool search engines to give better rankings to their pages. The techniques used in black hat SEO will not have any benefits to the users. Black hat SEOs can be spammers but employ other kinds of techniques too. Examples of some other kinds of black hat SEO techniques are: link farms, hidden text, scraping, doorway pages, cloaking, comment spam, paid links/content+, keyword stuffing, etc. Despite being unacceptable to the internet community, black hat SEO techniques are used because they work until the search engine finds out about them and lower awareness about the fact that search engines will ban their sites once they find out about the use of such techniques.