BH is things google frowns upon and will ban your for and white hat is things they allow and approve of.
Black hat are illegal and search engine can ban you if they can detect you that you're using a black hat while white hat is the illegal optimizing of a sites, or u are following to the rules and regulations of search engines.
Ethical SEO = White Hat = People who make decent sites with original, quality content and promote in honest ways. Unethical SEO = Black Hat = People who ruin the internet with 12,000,000,000 pages of garbage, and promote in shady ways.
One of the easiest way to understand is delivering similar webpages to visitors and search engines is whitehat whereas delivering different webpages to visitors and search engines is blackhat or cloaking is the actual term in this example
white hat seo wont take you anywhere... .. unless you have a good brand ... you'll need alot of efforts i'll prefer blue hat seo
what n3o says is right. Three way link exchange is not white hat, but people who get the first rank often do this. Blog comment for link building purpose even is not white hat, I think, although it's not black hat either. Even if you put your links in directory, that's not white hat. White hat SEO is trying to search natural links by link baiting and also article marketing. Remember why Google has a back link policy to modify its search engine? Because they want the most popular website get the first rank by telling other webmasters to give a "vote" to that website. They want "natural back links". So other than real natural back links can be considered as non-white hat SEO.