The term "radical Islamist terror" has been gaining a strange sort of currency on the right. It's a bad term and no one should be using it.
"Radical Islamic terror" is annoying enough, but you assume the people using it are distinguishing Muslim terrorists from other Muslims. (Though the question can be raised as to whether there is a moderate Islamic terrorist.) But "radical Islamist terror" is particularly bad because an Islamist is a member of a political movement advocating theocracy.
Is there such a thing as moderate Islamic theocracy? Our leaders believe that there is and use the term knowingly. They specifically want to distinguish the Muslim Brotherhood from its Al Qaeda splinter group, for example. This is a terrible position.
But people on the right generally would not argue that the Muslim Brotherhood is moderate or that we should be collaborating with any Islamist group. And so the term is being used mistakenly.
It's still an unhelpful term as it continues the trend of redefining unacceptable forms of behavior in the Islamic sphere as being less bad than the most extreme types of behavior. This is the kind of logic that gave us the moderate Taliban or Iran's new government.
Islamic theocracy is never moderate. It's the wellspring of Islamic terror.