Citing a source means that you show, within the body of your text, that you took words, ideas, figures, images, etc. from another place. They are a short way to uniquely identify a published work (e.g. book, article, chapter, web site).  They are found in bibliographies and reference lists and are also collected in article and book databases. 

Citations consist of standard elements, and contain all the information necessary to identify and track down publications, including:

• author name(s)
• titles of books, articles, and journals
• date of publication
• page numbers
• volume and issue numbers (for articles)

You must cite:

• Facts, figures, ideas, or other information that is not common knowledge
• Ideas, words, theories, or exact language that another person used in other publications
• Publications that must be cited include:  books, book chapters, articles, web pages, theses, etc.
• Another person's exact words should be quoted and cited to show proper credit 

When in doubt, be safe and cite your source!