Reference sources are authoritative books that assist you in finding/locating information about people, facts, and/or ideas. Reference sources (e.g encyclopedias, dictionaries, fact books, almanacs, biographies etc.) can be a great starting point for your research. They contains an overview of topics/subjects and enables you to find information when you don't know exactly what to look for; or want to explore a topic of interest & widen your knowledge. They are either used to get background information on a topic that you are researching or to find specific facts to support a point being made in a paper.
The Handbook of Artificial Intelligence by 