It has always been difficult, almost impossible, to reach a globally acceptable definition of terrorism. Historically, many terrorist organisations engaged in indiscriminate killing of random citizens, spreading chaos and fear. However, governments can also create and spread fear, lie, manipulate, and use the ‘politics of fear’ to restrict human rights, demonise opposition, limit, and even abolish democratic institutions to extend their grip on power. Authoritarian leaders have often stigmatised potential opponents, naming them ‘terrorists’. Some liberation movements, that in the past had radical fighters employing terrorist tactics, later denounced them and became acceptable and legitimate political actors. Therefore, terrorism is a crucial category to understand imaginaries and fears. This chapter explores the historical origins of terrorism, classifies various types, explains the role of religion and ideology, and provides various case studies to exemplify the imaginaries of terrorism and the politics of fear.