In recent years, we have witnessed an increase in terrorist activity, especially in the Middle East. This fact has increased academic and media attention to this circumstance, which has led to a proliferation of studies on this topic. This, unfortunately, has not been accompanied by a comparable increase in rigor in the treatment of basic concepts, which, in my opinion, makes it necessary to clarify terms such as fundamentalism, extremism, integrism, fanaticism or even terrorism.