Modern science makes great efforts to define contemporary terrorism. However despite the fact that terrorism represents a real plague for a contemporary society, the politics of many powerful countries delays to define contemporary terrorism in a generally acceptable manner since double standards are dominating factor. There are not good or bad terrorists regardless of the fact that the unprincipled interpretation of this phenomenon by the big powers misleads the public opinion in recognizing contemporary terrorism. Terrorist activities are never supported by population on a large scale as long as they are called terrorist. If they have a large-scale support, then they are not terrorism but guerilla or rebellion. When defining terrorism we must know that terrorists are unavoidably politically motivated, that they resort to violence, that the terrorist activities are directed towards far-reaching psychological consequences beyond a direct victim or target of an attack and that they must belong to some organization. It is also important to know that terrorist demands are never either realistic or legally based. Therefore, when defining terrorism it should take into account the importance of the definition of terrorism that would provide for the international cooperation as an objectification of the term, i.e. according to which the consequence is a condition without which there would not be a consequence (Condicio sine qua non). According to the results of his scientific and research work so far the author of this paper defines terrorism in the following manner "Terrorism is an organized use of violence (or threat with violence) by politically motivated individuals or groups who are determined to impose their will to the institutions of power and citizens through fear, fright defeatism and panic.".