".... any book not designed for consecutive or complete reading: a book to which you refer, usually very briefly, for a specific bit of information or a concise introduction to a topic."
Gore, Daniel. Bibliography for Beginners. New York: Appleton-Century-Crofts, 1973
Encyclopedia: A single or multi-volume reference work that provides general background articles on either a wide range of topics or a more specialized discipline.
Dictionary: Provides the meaning of words in a language or field of knowledge.
Handbook: A compact reference book providing essential information in a specific field of study.