A phrase that can be used as an exclamation when no other phrase will do, or as a question by someone who's really confused. Typically used as an extra addition to a statement/question, though sometimes used on its own.
Not to be confused with wtf or ftw. Possibly originating when a gamer wanted to to mix things up (or was so mad s/he messed up saying wtf.)
"I shot that guy in the head three times, and he still turns around and kills me?! TWF?"
"The what fuck/TWF!"