I want to know the answer to the following question:
What is it called when the last Imam or his unborn successor goes into concealment?
All the background I'm provided with is that "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.". Is that enough to answer the question?
Answer: no