A reference tool is any source of information. Books are reference tools. Libraries often have reference books such as atlases, almanacs, dictionaries, and encyclopedias. Usually, reference materials cannot be checked out of the library, but you can use them to look up information while you are at the library. An encyclopedia is a collection of articles, listed alphabetically, on various topics. "When you need information quickly, an encyclopedia is a good choice. Electronic encyclopedias, available on the Internet or CD-ROM, have sound and video clips in addition to text. A dictionary is an alphabetical collection of words, their spellings, their meanings, and their pronunciations. If you find a word you don't understand, you can look it up in a dictionary. Many dictionaries also include abbreviations and information about well-known people and places.