Satr (Arabic: ستر, lit. 'concealment') is a term used by the Isma'ili Shi'a for various periods in their history where the true imam was hidden (mastur) and represented through agents. These periods of concealment (dawr al-satr) might end with the renewed public manifestation of the imam, or continue until the present day. Entering into concealment did not mean that the line of imams stopped with the hidden imam; the Isma'ili concept is thus different from the concept of occultation (ghayba) as conceived by the Twelver Shi'a.