Here's a great definition of primary sources from the American Library Association
"Primary sources are original records created at the time historical events occurred or well after events in the form of memoirs and oral histories. Primary sources may include letters, manuscripts, diaries, journals, . . . memoirs, [etc]. These sources serve as the raw material to interpret the past, and when they are used along with previous interpretations by historians, they provide the resources necessary for historical research."
--Using Primary Sources on the Web, rev. 2008.