woohoo!
w00h00!
w00!
w00t!

Thats the evolution. I'm not going to go into fancy stories because thats how it came to be durring my time playing online. It predates most people ventures with the 'net, but it's meanings have been adapted in various ways.

Bottom line is it's an exclamation of excitment. That is and always will be the root definition of it.