After distinguishing between acts of terrorism and terrorist risk from a social psychological perspective, this paper focuses on the lay thinking about terrorism. We suggest an analysis carried out at the ideological/positional level of explanation, as opposed to the intra/interindividual level. This analysis is based on the Theory of Social Representations and its specific methodologies. It is supported by an empirical study completed on the airports of Marseilles-Provence (France) and Boston-Logan (United States). The study compared the lay thinking about terrorism among participants who had different levels of anti-terrorism practice (French safety officers vs. French passengers) and of personal involvement (US vs. French passengers). The social representation of safety officers had a more practical orientation. In contrast, for passengers, the lay thinking about terrorism was normative in nature and displayed a salient affective component. Moreover, in the group of US passengers, who reported higher scores of personal involvement, the element 'Muslims' appeared as central for defining terrorism. These empirical results illustrated a theoretical proposal according to which, in conflict, threat, or crisis situations, and in the absence of practice, high personal involvement may favour the expression of lay thinking through a more narrow, radical, collective and mobilising form, the nexus, rather than through social representations.