It's, uh, ( wow. how to explain it to someone who has never heard of it. someone who wields antique japanese weaponry and is from a similar world to the guy who didn't know what bullet trains are. ) It's like a dream. Only you're awake. And a computer generates what you see, instead of your brain. And you can manipulate it, kinda, instead of just... watching it?

This might be a situation where it's easier to show you than just tell you.