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.
Your favorite Star Wars Rebels heroes are ready to fight the evil Empire! Kanan, Hera and trusty old Chopper battle TIE fighters while Sabine uses her artistic talents to outsmart Stormtroopers. Zeb never misses an opportunity to take down troopers, and Ezra scores a special souvenir at the crash site of an Imperial fighter.