An exclamation of surprise, as if one is too startled or confused to finish one's sentence. When my little brother came home covered in mud, all our mom could say was, "What the?" A: "Oh, your phone bill came today. I think there's some overage charges on it." B: "What the?"
See also: what
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.