A primary source is an original document or other material that has not been changed in any way. It is a reliable first-hand account usually written at or near the time the event(s) occurred. Usually it was produced by someone with direct personal knowledge of the events that are described. It is used as an original source of information about the topic. Primary sources are distinguished from secondary sources. Secondary sources are documents based on primary sources. Thus, a memoir of a participant in an event is a primary source, whilst a history of that event based on several memoirs is a secondary source. Different kinds of work have slightly different definitions of a primary source. In journalism, for example, a primary source can also be a person.