Then there is the use of the term for rhetorical and political purposes... This is what obviously varies according to the interests of those using the term. Obviously the terrorists are always the 'other guys'.
Note that the definition I gave, which is nothing more than the Oxford dictionary one, includes a crucial word, "unlawful". This is very important to differentiate between warfare and terrorism. A sovereign state uses violence for political aims, this is warfare and it is 'lawful' (it may be unlawful under international law, though). This is why action by nation-states are usually not labelled 'terrorism'.
Note, have have worked with people assembling a major dictionary. They are just regualr people with regular foibles.
Just adding a bit more context as your previous comment seemed "sure" in that you're proclaiming "X is Y" while reality is not that black-and-white. Again, I agree with this and your previous comment.
Basic categorization of terrorism then would be concerned with:
a: tuple (agency, means)
must resolve to be "illegal" within the applicable legal scope. For example, a state dropping bombs on a civilian population (nation-state, war-crime) satisfies the above requirement but doing the same to enemy soldiers (nation-state, warfare) does not. Same with a private group blowing up a bank (ngo, crime).
b: tuple (target, reacting-agency)
Goal is to use terror in the target to induce the reacting-agency in responding in a desired manner. If there is no reacting-agency (and thus no goal) it is not terrorism; it is merely pathological.
Important to note that there is not one single definition of "terrorism" that everyone agrees on. For some, "terrorism" is a label assigned to your opposing groups, for others it's about violence for political or religious purposes. If it's from another nation-state, it's usually not labeled terrorism, even if it's against civilians for political/religious purposes. Some groups are labeled "terrorists" even without any recorded history of violence, and so on.
I'm not disagreeing with you, just adding that what "terrorism" is, is not as black-and-white as you put it.