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.
The Youtini Expanded Universe Ranking system is a 1-5 scale that ranks EU book quality, difficulty, and importance. Books closer to Level 1 are easier to read and understand, more important, and of higher quality.
The Legacy of the Jedi/Secrets of the Jedi omnibus contains the two young-adult stories written by Jude Watson telling the stories of four pairs of Jedi Masters and apprentices. Included as a bonus is the short story The Last One Standing.