Oral histories are usually interviews with people (also called informants or subjects) on a specific topic or topics. The interviewer is usually seeing first-hand perspectives on topics, activities, organizations, etc. Institutions usually require researchers to complete an IRB application just to ensure the research is documented.
Oral histories, just like the informants, can provide valuable information and insights, but they can also have errors and mistakes due to the frailities of human memory and inherent bias.
Interested in learning more about conducting oral histories? Check out the Oral History Association's site.