The study centers upon various definition of the concept of terrorism and different arguments. This study proposes the exploitation of the concept formation in philosophy and breaking up the concept of terrorism according to its principles. It also proposes the application of family resemblance structure as apposed to dominantly use of necessary and sufficient conditions. It tries to offer method that helps to better understand the concept of terrorism. It also tries to provide a guide that shows international organization how to examine the concept. In other words states understandings of terrorism may differ from each other although they resemble. This study shows that each state determines its own definition of terrorism according to its national interest. The concept of terrorism is socially constructed. Due to different reasons, and facts different states haven't reached to a common definition for terrorism.