A primary source is firsthand testimony or direct evidence concerning a topic under investigation. Primary sources are records of events as they are first described, without any interpretation or commentary. They are also sets of data, such as census statistics, which have been tabulated but not interpreted. Primary sources are original records created at the time historical events occurred or well after events in the form of personal memoirs or oral histories.
A secondary source is a work that interprets or analyzes Primary Sources. It often attempt to describe or explain primary sources or to use them to argue a contention or to persuade the reader to hold a certain opinion.
A tertiary source is a source that discuses or summarizes material published in Primary and Secondary sources.