Put simply, "20 Questions" is a website that requires you to think of anything you want, from a basketball, to music, or why not "everything"? It will then ask you various questions you need to answer as honestly as you can, and eventually, it will try to guess what you were thinking about after 20 questions. It works remarkably well, so why don't you give it a try?
By the way, I'm sure you'll find out why I put this in "Conspiracy" after you've played it a few times.
"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram