This is Internet for: You what, mate? This is universally used by internet speakers, regardless of weather or not they live in a society where the term "mate" is commonly used.
This is the word "what," except it is pronounced and written with more awe; said when somebody says something what is too shocking for the word "what" to be used
Pronounced as "wuut"
Doctor Emmett Brown: "I just built a time machine out of a DeLorean!