What is the difference between primary, secondary, and tertiary sources?
According to a guide created by the University of Maryland Libraries, primary sources are original materials that have not been subject to much, if any, interpretation or evaluation. Some examples would be a person's diary or journal, newspaper articles written at the time, photographs, interviews, and even Internet communications (such as email).
Secondary sources are materials that have been written or created sometime after the event and subject to interpretation or evaluation. Some examples may include biographies, journal articles, and textbooks.
Finally, tertirary sources are those which "consist of information which is a distillation and collection of primary and secondary sources." These would include many reference materials, such as chronologies, dictionaries and encyclopedias, and guidebooks.
Keep in mind that sources may overlap. For example, a webiste could be primary or secondary. A textbook could be secondary or tertiary. When in doubt about a resource, ask a librarian or professor for help.