To ruminate productively upon our subject, we must first define it. Terrorism: the use of violence and intimidation in pursuit of political aims. Terrorism is an extension of politic, as is war said to be. Terrorism might be said to be a small scale version of war. In the end, war and terrorism consist of destruction of life and property until the victims capitulate to the political will of attackers.
There is however, one signal difference: war is waged by states; terrorism may be pursued by smaller, less legitimate entities. Individuals, even. Or as in the case of Islam by members of a religion. The boundary seems a bit diffused. No matter; the foundation remains untroubled: Shed blood and destruction until you get your way. If the scale is large, call it war; if small, call it terrorism.
There is one additional factor: Organization. For the required political goals, there must be a political organization to pursue and operate it. Hence, a U.S. nutcase recruited and used by ISIS can honestly be called a terrorist; the same nutcase on his own, cannot. He (Or she, or it) is only a nutcase. American media reporters presently seem to be trouble by this. American lefty politicians, even more so.
Further, the internet provides such as ISIS the opportunity to preach to local nutcases, inciting them to desperate acts with no other connection between the two. Like passing a loaded gun on a table, picking it up and shooting someone with it. Is that organized? Well, if ISIS is trolling for and using such opportunities, it is certainly organized. A tool in pursuit of ISIS goals and certainly terrorism. It remains terrorism when the nutcase never contacts ISIS if he acts knowingly for ISIS goals as a volunteer.
Political leaders prefer to consider violence opposing their goals as terrorism, violence in favor of their goals, as tolerable. Black Lives Matter is ok; ISIS is not, but local ISIS type acts are ok until proven to be ISIS related. And even then, attributed to racism or some such if possible.
Never mind that no violence in pursuit of political goals is ever appropriate in a democratic polity. Such is an attack on the roots of democratic ideals. Any and all uses of political violence and intimidation should be extirpated root and branch without a thought if democratic government is in fact the goal.
The sort of selective reaction to political violence that we see is not only destructive of American values, it destroys any body politic in which it is allowed to endure.