That's actually a great question. I was thinking about it overnight. So let's see if we can find common group.

For simplicity, assume there's a group of 1000 people. We can obviously agree that if they're all violent, that's a riot. I hope we can also agree that if 1 is violent, it's not.

So, what about 10 out of 1000? I think not. What do you think?

This has actually been on my mind. Since we are talking semantics, I have a couple of questions for you:

1. Would you call the Fort Hood Massacre "work place violence" or a terrorist act committed by Islamic extremists?
2. How about the massacre in San Bernardino? "Man made disaster" or a terrorist act committed by Islamic extremists?

Or do you have some other word for these atrocities if you do not like any of the ones that I proposed?