What is White (or "White Hat") SEO

Opposite to "black" methods of a website optimization there is another set of methods named (surprise! surprise!) White SEO (or White Hat SEO).

So what are differences and why they are opposite?
Their targets are absolutely the same - to make a website visible in search engines and move it to the first page of google, yahoo, msn/live, altavista by defined search requests.

But the approaches and methods are different.
"White" methods are absolutely natural.
It is not a secret Google likes popular sites made for humans, not for search engines.
And a measure of popularity could be a number of incoming links that other websites place on their pages. A link is considered as a "vote".
So "white methods" include creating a websites, placing popular materials, making them popular so other people would be happy to put links to our website on their ones.
It is easy!

And it is the way google recommends us to go.
I found my old sites suddenly have high PR (page rank) and appeared to be on the first pages by their particular requests absolutely with no any special steps done!
That's really amazing, and it is the ideal way that definitely works in an ideal world.