can anyone ple tell me what "is the keystone of statistical testing" ?

Answer 1

Might be this. Check the website for more info.

Hypothesis testing often confuses people but it is the keystone of most statistical applications. Every acceptance sampling test, designed experiment, and control chart* is a statistical hypothesis test.

Answer 2

Never heard that phrase, but I'd guess it is the chi-squared table, that tells you the statistical significance of your results.

What I mentioned is a small part of ghoulie's answer. Now that I read it, I like his better--pick him.