occultation

[T]he diſtance of any place within this kingdom from it, will not much vary the manner of their Appearance in any of the Phænomena, except the Eclipſe of the Sun: for, in the Occultations, the Stars will appeare to paſs nearly under the ſame Angles and Spots of the Moon; […]

If Mr. [Thomas] Campbell's poetry was of a kind that could be forgotten, his long fits of silence would put him fairly in the way of that misfortune. […] [T]he re-appearance of such an author, after those long periods of occultation, is naturally hailed as a novelty—and he receives the double welcome of a celebrated stranger and a remembered friend.

We are therefore, constantly hoping for the joy and happiness, personified in Imām al-Mahdi, the Imām who is alive at this very time, and who is himself awaiting the command of Allāh to reappear, so that he may strengthen the weak, and judge the oppressors. He will reappear "without having done Bay'ah to any oppressor". He went into occultation because he did not want [to] submit to any unjust ruler.