BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
The Battle of Endor was never fought—it was just so much Alliance propaganda. At least, that's the lie being spread by the Ante-Endor Association. But Wedge Antilles and his Rogue Squadron comrades know the truth. They were at Endor when so many gave their lives to destroy the second Death Star. And so, for those lost friends, this is a battle they will not lose.