In the nineties the FBI categorized things like church burnings as acts of terrorism, understandably so. (and that's an important example, as there are depressingly many church burnings every year)

I'm pretty sure those sorts of crimes still fall under the FBI's terrorism label but their political masters don't really play that up. "Violent crimes committed by people who are not like you who we'd like you to hate" is as accurate a definition of terrorism as anything at the political level, nowadays.