bpicolo has provided the proper link, though the quick answer is "someone who plays the game Kerbal Space Program".
The less serious answer is "somebody who routinely experiences the joy of rapid unscheduled disassembly in their virtual creations".
My favorite videos of his are not the ones where he shows off new video games, but the ones where he delves into space history and engineering and astrophysics. He's taught me so much!