"1. someone or something that provides what is wanted or needed; 2. the cause of something (such as a problem) 3. a person, book, etc., that gives information" (http://www.merriam-webster.com/dictionary/source)
In academic writing, sources are the materials from which the writer gathers information. It is important that you evaluate the sources of your information to be sure that each source is accurate, relevant, current, objective, and authoritative. For more information on evaluating resources, visit the Evaluating Resources page.
When researching a topic, you need to investigate a variety of sources to gather information. This may include: