"FTW" is an abbreviation that means "for the win." It is used as a type of shorthand on the Internet and when texting as a way of expressing enthusiasm. Normally used at the end of a comment, FTW is sometimes meant to be sarcastic although it is also often genuine in nature.
The origins of "for the win" stem from the television game show "Hollywood Squares," in which contestants tried to complete a tic-tac-toe formation by choosing celebrities to respond to questions asked by the host.
When contestants were ready to make a choice leading to a potential win, they or the host often stated the name of the celebrity chosen to answer the question followed by "for the win." For example, "I pick Charlie Weaver for the win."