exaggeration of the word "what", which expresses an interrogative attitude of the speaker, in many ways.
"the fuck" -part is exchangable with "the hell", "the heck", etc.
"what" is exchangable with "who", "where", "when" etc.
What is that? - What THE FUCK is that?
What has just happened? What THE FUCK has just happened?
What is your name? - What the fuck is your name?
What are we going to eat tonight? - What the fuck...