A version of a book that's shorter than the original is an abridgment. That tiny reference book you can fit in your pocket is an abridgment of the enormous tome your parents keep on a wooden dictionary stand.
There are a lot of abridgments in the world of audiobooks. If you don't have 33 hours available to listen to George Eliot's Middlemarch, you might consider an abridgment that captures the basic story in under three hours. You can use this word to describe the work of shortening a longer work, too: "The abridgment of my life story is proving much more challenging than I expected." Abridgment comes from a root that means "short."