Nass (Arabic: نَصّ, romanized: naṣṣ) is an Arabic word variously translated as "a known, clear legal injunction," a "divine decree", a "designation", "written law" as opposed to unwritten law, "canonical text" that forbids or requires,a "textual proof". In Shiah Islam (Twelver and Isma'ili), nass refers specifically to the designation of an infallible Imam by a previous infallible Imam.