In intellectual-political and security circles extremism is a frequent topic, and that is good, because every responsible discussion of important social phenomena may contribute to their better understanding. Unfortunately, this socially beneficial and cognitively productive effect of a debate mainly is not visible, but most often it is politically instrumentalized, which is done by those who aggressively impose their views. Thus extremism, as an insufficiently delineated and defined term in contemporary political practice, turns into a pejorative disqualification. The first important feature of the term extremism is its original multi-meaningfulness. In contrast to other terms, often thoroughly defined and delineated, it has retained all of its original meanings, and at the same time, with the development of the milieu where it existed and in particular after entering the area of politics, it has acquired also a new meaning. In such a way, the door was widely open for different interpretation of this phenomenon. In turbulent times that, from the aspect of security in particular, have an effect on the comprehension and delineation of the terms extremism, terrorism, terror, and similar ones, it is of critical importance to correctly determine the afore-mentioned terms. In this context, it would be necessary to make efforts to more clearly define what is socially undesirable or dangerous in the area of thinking and behavior. To define these social phenomena is not at all risk-free, because the one who has 'charismatic power' to define what extremism is, determines also who will be the target of this 'inquisition'. Thus, a vague definition, which suits one side, may be used, as desired or required, to slander political opponents in particular.