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.
Discover – or rediscover – these stories written shortly after the release of the motion picture The Empire Strikes Back: Imperial officers plot against Darth Vader, Leia fights alone on a world that has never felt the Empire's threat, Lando Calrissian and Lobot battle to save their beloved Cloud City and many more. It's a big galaxy, and these adventures go far beyond what you saw in the films!