Wiktionary
alt. (context Internet slang English) Being the best; being great, awesome, amazing or spectacular; sure to succeed ''(used as a term of approval, similar to (term: long live))'' prep.phr. (context Internet slang English) Being the best; being great, awesome, amazing or spectacular; sure to succeed ''(used as a term of approval, similar to (term: long live))''
Wikipedia
For the Win is the second young adult science fiction novel by Canadian author Cory Doctorow. It was released in May 2010. The novel is available free on the author's website as a Creative Commons download, and is also published in traditional paper form by Tor Books.
The book is centered on massively multiplayer online role-playing games. Even though the novel is targeted toward young adults, it takes on significant concepts such as macroeconomics and labor rights. It covers the new and fast evolving concept of virtual economy. It also deals with MMORPG specific topics like gold farming and power-leveling.
Usage examples of "for the win".
He used his dementia monsters to soften up and distract an opponent, then moved into melee for the win.
Lisseut, who, wisely or otherwise, had not gone home for the win.
The combined rank of Zecha's pieces in it easily surpassed his, so she could claim it for the win if she wanted.
We hesitated, at that tense point when the gambler at the craps table breathes on the dice, then clutches them in his hand for a single, heart-stopping instant, asking for the win.