This is the 9991st most frequent Russian word.
апокалипсиса
"Apocalypse" or "end of the world."
The word "апокалипсиса" is used in its genitive case indicating relation or subject of the predictions.
Он читал книгу о предсказаниях апокалипсиса.
He was reading a book about the predictions of the apocalypse.
The word "апокалипсис" is in its prepositional case, used after the preposition "после" to indicate an event.
После апокалипсиса мир изменился навсегда.
After the apocalypse, the world changed forever.
The word "апокалипсиса" is again in the genitive case, specifying the subject of prevention.