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.
Accompanying Hoole on his study of the B'omarr monks at the palace of the nefarious Jabba the Hutt, Zak and Tash are astonished to learn that the monks are spidery, disembodied brains, one of whom wants to learn about the Force.