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.
With resources vital to the Empire on the line, Vader makes his move...but Cylo and his forces are looking to show him up before he can! Full-scale warfare on the surface of Sho-Turun!