A reference source is something you REFER to (hence the name), or consult, for short pieces of information or a brief overview of a topic
They provide statistics, facts, and figures in an easy to find format.
They can be in print or online, or both.
Print reference sources contain an index at the back of the book to lead you to the specific information you want. This is the print version of a search engine, but much more efficient and targeted. Always start with the index.
They can be general, like the Encyclopedia Britannica, or subject specific, like the Digest of Education Statistics or the Rolling Stone Encyclopedia of Rock & Roll.
They are generally the most objective information source, since they are designed to provide information, not persuasion or analysis.
Print reference sources are located by call number throughout the library and cannot be checked out. You can photocopy the pages you need from them.