Background information can be found in:

• textbooks
• dictionaries
• general encyclopedias
• subject-specific encyclopedias 

Why use background information? Background research:

• Provides a good overview of the topic if you are unfamiliar with it.
  (example: a student doing a market research report on a company using a business research database to lookup information on a particular basis)
• Helps identify important facts -- terminology, dates, events, history, organizations, etc 
  (example: a student writing a literary analysis paper using a dictionary of literary terms)
• Can help guide your thinking on a topic by providing a foundation. 
  (example: a student completing a mock policy brief on fracking in Pennsylvania consulting a dictionary of environment and conservation)
• Leads to bibliographies which provide additional sources of information.
  (example: a student writing a literature review on clinical treatment of postpartum depression researching the history of postpartum depression in a psychology encyclopedia)