When ravers find themselves in a state of effervescence born in a Dionysian spirit, they produce things they cannot explain: thoughts with neither end nor beginning, bodies bending in eccentric lucidity, an orgy of feelings and emotions with no reason, ground, or precedence …
When State officials find themselves in an orgy of effervescence born of the politics of death, they produce things that must not be explained: terrorism.

I happen to think terrorism is a adequately well-defined by sort of inspecting the word itself: terrorism is any systematic (thus the "ism") act or acts that are meant to inspire a particular emotion - terror. The most bizarre facet of terrorism is that it's a crime of inflicting an emotion, an affective crime. For example, it's rare to have inflicting emotions be criminalized - the police tend not to drag people away to jail for inflicting joy upon someone, or remorse, contempt, lust...

Some discourse-theory light maybe? As in: rather than describing an actual object (a particular form of practice that terrifies people, which leads into all sorts of debates about who can be a terrorist, is the pervasive violence enacted by men against women 'terroristic', is the precarised labour market a form of structural terrorism, etc), 'terrorism' may be seen as a disciplinary term in political discourse that serves to delegitimate political violence usually (but not always) enacted by the weaker actor in a given conflict.

'Terror' incarnates when somebody is terrified, and so takes as many forms as there is experience of terror. There is no meaningful definition beyond the subjective state of feeling terrified so there is no thing to be objectified here

What more needs to be said? All the rest seems to me to be propaganda and excuses for a terrifying worldview.

Somone in the field of linguistics, probably someone really important, but for once NOT Naom Chomsky, said: "language is a dialect with an army and a navy" - along this same line of reasoning,

"terrorism is terror with an army and a navy"