This refers to a sort of cosmic memory of all which has been. Edgar Cayce said that the source of his readings was the Akashic records.
Rudolf Steiner says the following of Akashic records:
...man can penetrate to the eternal origins of the things which vanish with time. A man broadens his power of cognition in this way if he is no longer limited to external evidence where knowledge of the past is concerned. Then he can see in events what is not perceptible to the senses, that part which time cannot destroy. He penetrates from transitory to non-transitory history. It is a fact that this history is written in other characters than is ordinary history. In gnosis and in theosophy it is called the "Akasha Chronicle"...To the uninitiated, who cannot yet convince himself of the reality of a separate spiritual world through his own experience, the initiate easily appears to be a visionary, if not something worse. The one who has acquired the ability to perceive in the spiritual world comes to know past events in their eternal character. They do not stand before him like the dead testimony of history, but appear in full life. In a certain sense, what has happened takes place before him.'
See Steiner, Rudolf