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.
Disney/Lucasfilm Press have released several middle-grade novels leading up to each of the Sequel Trilogy films, and have been wonderful contributions to Star Wars storytelling. They even feature several illustrations by legendary comics artist Phil Noto! Justina Ireland's book fits into the Journey to The Rise of Skywalker publishing program as a prequel to Episode IX. This book feels like exactly what we’ve been waiting for, as it places Rey, Rose, and Poe on a quest for the Resistance including a battle against the First Order, classic Star Wars creatures, and even a superweapon. Although billed as a middle-grade novel, you’ll be disappointed if you skip it, no matter your age!