The phrase "original negative" refers to the first film or image that was created directly by the camera. It is the initial version that can be used to make copies or prints. Full definition
Gelatin silver print, Posthumous print made from original negative on the occasion of the Garry Winogrand exhibition organized by the National Gallery of Art and the San Francisco Museum of Modern Art, courtesy Center for Creative Photography, The University of Arizona. (brooklynrail.org)