Generally stands for 'What the fuck'. Most people use a question mark afterwards to get the point through. Rather than using the same term for the other 'w's, who, when, where, and why, it makes more sense to actually state the word and follow it with 'tf'

Capitalization doesn't really matter.
This term can also be likened to 'What the shit?' which is more comical and has a tantamount meaning.

The World Taekwondo Federation.
WTF, holds many competitions throughout the world.

Denotes: What the Fuck!

1. What the fuck.
2. World Tae Kwon Do Federation

Stands for What The Fuck.

Wat The Fuck

used in instant messaging when somthing is random also c LMAFO

The universal interrogative particle.

The abbreviation of, most commonly, 'what the fuck', though sometimes also 'who/why/when/where the fuck'. When used with an exclamation point instead of a question mark, it becomes an exclamation of amazement, confusion, disbelief, ect.

Both forms are often accentuated with 'mate' or preceded by 'dude'.