An encyclopedia is a reference source that provides information on many different subjects. It is divided into multiple volumes that are organized alphabetically to make topics easy to find. Each page lists subjects in alphabetical order along with guide words. To look up a topic, one finds the letter it begins with and chooses that volume. Print encyclopedias contain physical books, while online encyclopedias provide digital information. The encyclopedia is a valuable resource for finding answers to questions by locating the relevant topic or key terms.