"A primary source is a document, image or artifact ... created contemporaneously with the event under discussion." (Williams, Historian's Toolbox, 2nd ed., p. 56)
Primary sources are original sources, in which its witnesses or first recorders describe a time, person or event.
Depending on your topic, it may be a diary, a letter, published memoirs and other source documents from the period of study, as well as electronic, microfilm, and printed collections of these documents published at a later date.
For more information, go to the guide, Primary Sources.