revealing or disclosure of religious truth

Revelation is when something is made clear or obvious that was hidden before. Most of the time, the term is used to speak about religious revelations. That means that the revelation is done by communication with the divine. Revelation can be through a deity who may send a messenger. Messengers that are supernatural are often called angels (Angel literally means messenger). Human messengers tend to be called prophets.

The Bhagavad Gita is said to be Krishna's counsel to Arjuna.