You might have heard people discussing the upcoming Battle of the Bastards in Game of Thrones Season 6. And you might be confused. While fans of the HBO show who have not read George R.R. Martin's books are probably used to being confused by the speculations and grievances of book fans, even those who have read the book are probably flummoxed about the so-called Battle of The Bastards. I have an explanation, but I want to preface it with a SPOILER ALERT for both the upcoming season and the book A Dance With Dragons.
For all those who are confused, the Battle of the Bastards is speculated to be the climactic battle of the upcoming sixth season of Game of Thrones. Sources have told the blog Winter is Coming that the ninth episode of the upcoming season will allegedly feature a battle between Jon Snow and Ramsay Bolton. Because Ramsay Bolton is the bastard son of Roose Bolton and Jon Snow is Ned Stark's bastard, fans have called it the Battle of the Bastards. Reportedly, Jon Snow will lead the wildlings, while Bolton will lead the Karstarks and Umbers. Sansa Stark has been spotted on the set as well, suggesting that she will be involved. Other intel gathered by the blog Watchers on the Wall has revealed that at least one giant may be involved, no White Walkers have been spotted, and there will (surprise, surprise) be a lot of death at this battle.
The reason fans of the books might be confused is that the Battle of the Bastards hasn't happened in any of the books... yet (get on that next one, GRRM). Instead, it is hinted at at the end of A Dance With Dragons, the most recently published fifth book in the Song of Ice and Fire series. The book ends with the delivery of a letter from Ramsay Bolton to Jon Snow, known to fans as the Pink Letter or the Bastard Letter. Here's the last paragraph:
I want my bride back. I want the false king's queen. I want his daughter and his red witch. I want this wildling princess. I want his little prince, the wildling babe. And I want my Reek. Send them to me, bastard, and I will not trouble you or your black crows. Keep them from me, and I will cut out your bastard's heart and eat it.
The letter informs Jon Snow that Stannis Baratheon, Snow's ally, is dead at Winterfell. Bolton demands the return of his bride (a bride who on the show, but not in the books, is Sansa Stark) among others, threatening war and death if they aren't returned to him. Snow does not believe the letter to be factual, and ends the book heading to Winterfell aided by wildings. As he leaves, he is stabbed, which is his final scene in the fifth season of the show and the most recently released fifth book.
It seems likely that the Battle of the Bastards is the meeting of the resurrected Jon Snow and Bolton that is prompted by the letter. Since it's where both the last season and last book left off, it's one the biggest mysteries in the show so far. It's still ambiguous whether the new season will come out before the new book, so we don't know where we'll get our answers. Update: GRRM confirmed in a blog post that Winds of Winter will not be out until after the Season 6 premiere. It's also important to remember that the show might be veering away from the books at this point. All I can say with certainty is that we're in for some bloodshed.