The concepts like human rights، terrorism، right to development and security، are the issues of gray-area phenomena in international system. This paper is the result of a research programme on the topic of international criminal justice at the Hague Academy of International Law. Regardless of the matter of coming up with an ironclad definition of terrorism، we all need a basic and universal conceptual underpinnings of the Law and criminology of terrorism. The author is looking through the appropriate method to gain a new definition. He examines the sources like doctrine، international and regional contract، Security Council and general assembly’s resolution to answer this question. He believes that redefining international terrorism needs a synthetic definition of political science and international Law which involves all the common and key standards of international community as a whole.