From HIstory Liaison Brian Jirout's Primary Resources guide:
Primary resources (or primary sources) refer to documents or other items that provide first-hand, eyewitness accounts of events. They are created by witnesses or recorders who experienced the events or conditions being documented. Often these sources are created at the time when the events or conditions are occurring, but primary sources can also include autobiographies, memoirs, and oral histories recorded later. Primary sources are characterized by their content, regardless of whether they are available in original format, in microfilm/microfiche, in digital format, or in published format.
Examples of primary resources:
Primary sources are different from secondary sources, which are written later and usually comment on or analyze historic events or original documents.
To find out more about finding primary sources, check the Primary Resources LibGuide.