All academic libraries use a classification system called the Library of Congress, or sometimes called the LC system, which is an alpha-numerical system of organizing books. Essentially, these letters and numbers are like the address of where a book lives and are arranged by their subject. This means that when you find a book, the ones next to it will be about the same subject content, or what they are about. This is super helpful when trying to find books on your topic since books on your topic will be grouped next to others on the same or similar topic.