These irrevocable licenses are used to define how the narrator, as the copyright holder, would like the general public, rather than a specific party, to be able to make use of their oral history materials. Further information on specific types of Creative Commons licenses is available at creativecommons.org. See more on the case for Creative Commons in oral history work here: https://ohda.matrix.msu.edu/2012/06/a-creative-commons-solution/