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 hotshot Resistance pilot Poe Dameron captured by pirates, it's up to BB-8—and Rapier Squadron—to save the day