Encyclopedias contain factual articles on many subjects.
There are two types of encyclopedias -- general and subject. General encyclopedias provide overviews on a wide variety of topics. Subject encyclopedias contain entries focusing on one field of study. Encyclopedia entries are listed alphabetically, much like a dictionary. For multi-volume encyclopedia sets, use the index located in the last volume to help find articles on your topic within the encyclopedia.
When to use an Encyclopedia:
when looking for background information on a topic
when trying to find key ideas, important dates or concepts
Examples of Encyclopedias:
Encyclopedia of Careers and Vocational Guidance (subject encyclopedia)