The American Heritage Dictionary of the English Language defines an encyclopedia as: A comprehensive reference work containing articles on a wide range of subjects or on …numerous aspects of a particular field, usually arranged alphabetically. .
In these days of instant Internet research, many people have forgotten (or never even knew) the differences between an encyclopedia, a dictionary, an almanac, an atlas, etc. To read more on the ins and outs of the fascinating world of encyclopedias, see Answers.com via the Related Link. ( Full Answer )