Terrorism has characteristics of diversity and complexity in means, forms and purposes of action. Terrorism triggered by religious ideology has been defined differently in the history, politics, and social environment of each country. Also, the types of terrorism can be classified as revolutionary, political, eco, nationalistic, State-Sponsored, religious and criminal terrorism. Moreover, Western media generally use a mixture of terms such as revolution, guerrilla, crime and terrorism. In particular, it is difficult to define a consistent concept of terrorism, as justification in the moral aspect is raised in these diverse and complex concepts of terrorism. Today, the scope of terrorist activities is spreading internationally and international cooperation is required to respond to them. However, the lack of a consistent definition of terrorism in the international community does not allow international cooperation to work properly to counter terrorism at the international level, and the punishment for terrorists is inconsistent. Many countries are attempting to agree on terrorism laws stipulated in other countries. However, understanding the origins, diversity, complexity, and modern perspectives of terrorism and clarifying the concept must be prioritized before stipulating terrorism laws. Therefore, in order to establish the concept of terrorism that can be universally accepted by the international community, an in-depth review of various factors that makes it difficult to establish a consistent definition of terrorism at the international level is required.