So this is problematic to compare The Reign of Terror to Terrorism and modern terrorism. The Reign of Terrorism is more akin to an act of "political genocide" (some arguments have been made to mark political purification as a from of genocide, something I disagree with) rather than "terrorism" even of the late 19th century type.

Looking at Terrorism from the 19th century, one thing is common, political assassinations either in the name of anti-monarchism or anarchism. Taking the assassinations of Czar Nicholas II and William McKinnley, these are targeted attempts to kill a specific individual and this style of assassination will culminate in the assassination of Archduke Ferdinand.

Then compare this contemporary/modern terrorism which (regardless of the origin, purpose, or ideology of the act) is focused on harming the populace and creating fear to sway political groups into acting in specific ways. The "Reign of Terror" created fear for the purpose of "finding enemies of the Revolution".