The United Nations had difficulty in drafting a definition of terrorism because the characteristics of terrorism are hard to define.
There isn't exist a current agreement pertaining to a universal legal definition of the term terrorism. However, there has been some debate regarding the possible existence of an, at least partial, customary definition of terrorism.
To define the term terrorism it is necessary to take into account the following key elements:
1. the perpetration of a criminal act (such as murder, kidnapping, hostage-taking, arson, and so on), or threatening such an act;
2. the intent to expand fear among the population which may cause public danger or directly or indirectly coerce a national or international authority to take some action, or to refrain from taking it;
3. when the act entails a transnational element.