It does have a useful definition I think in “a non-state actor using violence to serve some political goal”, as that at least lets one categorize a murderer who just hated that specific guy as having something different going on with them compared to a murderer who wants their act to shock a nation into taking some action. It’s commonly misused as “someone using violence that we don’t like”, but there is still some utility in understanding a person’s motive for doing something.