White Hat SEO refers to the usage of optimization techniques for the human audience. White hat SEO are ethical practices or techniques, like securing inbound links, creating quality content, using keywords, etc., that are designed to garner organic search traffic.
Black Hat SEO, sometimes referred to as webspam refers to the unethical practice of using tactics outside the a search engine's (or Google's) Webmaster Guidelines. This technique yields fast but short term results by raising the website's search engine result page ranking unethically or illegitimately by lowering the ranking of a competitor site.