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.
CASINO ROYALE! HAN SOLO gets demoted for insubordination – dragging his fellow cadets down with him. They go from flying TIE fighters to flying a giant cargo ship. Han's expert flying cuts their cargo ship's flight time in half, allowing them to stop at a casino for some hard-earned R&R. But Han's fellow cadets quickly learn this little "vacation" was NOT authorized by the Empire and, thanks to Han, they're all considered AWOL!