"Primary sources are materials produced by people or groups directly involved in the event or topic under consideration, either as participants or as witnesses."
(Quoted from: A Pocket Guide to Writing History, 5th ed. Boston: Bedford/St. Martin's, 2007)
Examples of primary sources, both print and online, include:
Materials which have not been interpreted by another person. Original document/writing created at or near the time an event occurred. Primary sources provide first hand accounts of experiences or events. Information is generally presented in its original form, whether it be a work of literature or art, or an account of an event or experience, or original documents or research products such as interviews, speeches, questionnaires, letters, diaries, manuscripts, memoirs, etc. Includes books, periodicals, and web sites.
Secondary sources provide second hand accounts of events. These sources include materials that have been reported, analyzed, or interpreted by people who do not have firsthand knowledge of an event and may be found in books or periodicals, or on web sites.