Task: Question Answering
Input (English): Passage: Within Shia Islam (Shiism), the various sects came into being because they differed over their Imams' successions, just as the Shia - Sunni separation within Islam itself had come into being from the dispute that had arisen over the succession to Muhammad. Each succession dispute brought forth a different tariqah (literal meaning 'path'; extended meaning 'sect') within Shia Islam. Each Shia tariqah followed its own particular Imam's dynasty, thus resulting in different numbers of Imams for each particular Shia tariqah. When the dynastic line of the separating successor Imam ended with no heir to succeed him, then either he (the last Imam) or his unborn successor was believed to have gone into concealment, that is, The Occultation. Question: What is it called when the last Imam or his unborn successor goes into concealment?
Output (English): The Occultation