The goal of this research is to draw dimensions of documentary cinema in the form of presenting clear and precise definition of that to yield the possibility of studying, knowing and classifying the works. At present, several definitions exist which are not comprehensive. The main issue is the disambiguation of these definitions. The root of the disagreement is the ambiguity of the concepts used in the definition of documentary cinema. This research has been conducted with the qualitative method and using deep interviews. The data was collected through interviews and documentary method. These data cause the extraction of obvious and hidden concepts in different definitions of documentary cinema. The analyses show that there does not exist an acceptable definition that is comprehensive. These definitions have been based on the concepts of truth and reality and which are not considered credible concepts to express the identity of the documentary cinema, per se. Other concepts, such as narration, should be added to the definition to attract the agreement of most of the experts, in addition to the induction of transparency. As a result, documentary is the film-maker’s cinematic narration of the world made on the basis of the evidence and documents and what he/she believes in as the real matter.