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.
Legacy's end begins! As Vader takes his place in command of the Emperor's secret Inquisitorius Program, he sets his sights on one of the most dangerous Jedi remaining alive…and it's not who you'd expect.