Twitch Plays Pokemon is a social test where you can go on Twitch (the livestreaming place) and insert chat commands to play Pokemon Crystal.
For example, if you type in left in Twitch Chat, Ethan moves left. If you type in A, Ethan presses A. Seems simple, right? Try this when there are 70,000 people doing this all at once.
This is a test of the Infinite Monkey Theorem which states that a monkey on a typewriter pressing random keys will surely produce one of Shakespeare's famous plays. This is a mathematical equation with small probability, and not actually monkeys. :P
...except this isn't Shakespeare, but playing a video game.
Try it out here!