General Discussion

And very often we don't like what falls under the meaning of a word and what doesn't.

This pretty much sums up my understanding of the difference:

The use of violence or the threat of violence, especially against civilians, in the pursuit of political goals.
The act of terrorizing, or state of being terrorized; a mode of government by terror or intimidation.
The practise of coercing governments to accede to political demands by committing violence on civilian targets; any similar use of violence to achieve goals.

You go and kill 20 people because it's a gang fight or you're pissed off and just want people dead or want vengeance, you're a murderer.

You go and kill 1 person to make a statement and scare the government, populace, or some defined group to bow to your demands or at least pay attention, you're a terrorist.

The more I hear the less I can determine a personal grudge that motivated Mangione to kill the UHC CEO. It's more like he's striking a symbol to promote change and rouse the masses. I've come to think that Mangione was a domestic terrorist. But not ruling out (just?) mentally ill. I'm undecided as to whether one can simultaneously be both--sometimes it strikes me that domestic terrorists are all a bit deranged by default and their derangement just settles on an ideology and ideologically motivated target to externalize their internal hate and anger.

Where that bleeds into the Covenant school's killing requires some careful splitting of hairs but I haven't seen the relevant manifesto and apparently nobody wants us to see the entire thing; moreover, at times a grudge acquires ideological clothing, muddying the waters even more until they're a slurry.