[kskz]

This is akin to stating that "public static void main(String[] args)" is complete nonsense when one didn't take the time to learn a little Java first.

The linked formula has been completely removed from its context

http://en.wikipedia.org/wiki/Averaged_one-dependence_estimat...

Below the formula in the page, you see everything defined and logically derived, and a brief overview of what it's supposed to do. You are correct in that Wikipedia may not be the best place to learn from scratch if you are a novice, but its purpose is more to be a concise reference than a thorough introduction.

If you need more guidance, there are thousands of textbooks at all levels of understanding, and if you opened a single one of them, you would immediately see that the "P" is standard notation for (conditional) probability.