Difference between retail & nulled

I hate to be the n00b here, but what exactly is the difference between nulled and retail, and why does nulled help or why do they do it?
Answer #1
no idea what u r talkin about
Answer #2
try http://en.wikipedia.org
Answer #3
Nulled = The protection is removed so you can use it freely.
Retail = Just how you get it when you buy it with protection and so on.
Moving To Helpdesk ~ ~