This article - a chapter from the author’s upcoming book on sectarianism - attempts to build fundamental conceptual idiomatic distinctions between the intertwined meanings of the words: sect, confessionalism and sectarianism. The author explores related concepts such as identity, belonging, sect, difference, fanaticism, and others. He also analyzes the linguistic and semantic evolution of the term sectarian in classical Arab thought, as well as the evolution of the related notions of sect, confession and craft (hirfa) that reflect on the ways of craftsmen, professions and Sufi’s regroupments in the Islamic society. This will lead him to examine the actual significance of the term sectarianism ta’ifiyya used in modern Arab language - sectarianism being a modern term and sect ta’ifa an old one. By opening a debate on the modern Western sociological concepts of sectarianism or al-firqiyyah, the study attempts to develop the concept of sect ta’ifa as a sociological tool able to analyze the formation, characteristics, and evolution of the new contemporary imagined communities.