The Akasha is the metaphysical term for what some call "The All", "Ether", "Cosmic energy", "The force" etc. And is the very essence for the energy that pervades the Universe. In scientific terms, this energy is referred to as "Quantum fields". If you haven't already read it, "The Tao of Physics"  by Fritjof Capra, will give you an in depth insight to the exploration of parallels between what is considered mysticism, and modern physics. Time and time again, modern science "Proves" what Witches and alike have always known.

It is believed that everything that happens, on every level, to everything in existence, is a manifestation of energy within the Akasha. Many liken it to the ultimate cosmic library where all information is stored, not just of the past, but of the future, and the endless possibilities there in.