means A sudden, striking disclosure of something previously hidden or unknown, especially a truth that arrives with a jolt of clarity.

from From Latin revelare, "to unveil" — literally re- (back) plus velum (a veil or covering), so a revelation is the moment the curtain is pulled aside. It entered English through Old French in the medieval period, carrying heavy religious weight: the last book of the Christian Bible is the Apocalypse, or Revelation, where hidden things are finally laid bare. That same velum gives us "veil" itself, and the sense of unveiling has clung to the word ever since.