Most people know computers run applications. So I say there's MAME, and I tell them what that stands for, and then I say it's an application that plays those games, the original, ARCADE versions.
As for building a cab or contol panels, I say it's because I hate using a keyboard, and gamepads blow; or that in some cases, the game is unplayable, or just sucks to play, without the original controls (like Star Wars).
People don't need to know how it works. Just that it does, and you like it that way.