What is the comparison distribution and why is it important in hypothesis testing?

I searched Google under the key words "comparison distribution hypothesis testing" to get these possible sources:

http://www.google.com/search?client=safari&rls=en&q=Comparison+distribution+hypothesis+testing&ie=UTF-8&oe=UTF-8

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.