Existing definitions of terrorism are not unanimously identical, as we shall see here comparing a Webster from 1948, 1981 and 1997. The way in which the EU and the FBI define "terrorism" are also strikingly different. I discuss the difference in the approach to the concept. Finally, I give a overview of the history of the term and of the phenomenon it is supposed to describe.

EU Law:EUR-Lex - 32002F0475 - EN - EUR-Lex (europa.eu)

US Definition of Terrorism:U.S.C. Title 18 - CRIMES AND CRIMINAL PROCEDURE (govinfo.gov)New November 2020 FBI document regarding "domestic terrorism":Domestic Terrorism: Definitions, Terminology, and Methodology — FBI