A used book or secondhand book is a book which has been owned before by an owner other than the publisher or retailer, usually by an individual or library. Used books typically become available on the market when they are sold or given to a second-hand or used book shop, they are usually sold at a discount price of what they were originally bought for, rare books might sell for more than their original price. Though the original authors or publishers will not benefit financially from the sale of a used book, it helps to keep old books in circulation.
Buying and selling old used books can be quite meaningful: selling them earns you extra pocket money; buying them saves you a great amount of money. And, most importantly, you save the earth by cutting less trees!