The Matrix

From the introduction:

Welcome to The Matrix! You picked a doozy of a place to come to for ten years, that's for certain. There's all kinds of mind-screwy questions and concepts going on, especially surrounding the eponymous 'Matrix'.

What is the 'Matrix'? It's like a large simulation system for over seven billion people, all hooked up into tanks and kept inside a virtual reality that uses a body's electrical and thermal energy along with a fusion process to create all manners of energy, for the sake of the Machines that now run the planet. It's a very strange, symbiotic relationship that they have going on here, especially since most humans don't even know they're in a simulation.