Definition - What does Akasha mean?
Akasha is a Sanskrit word that can be translated as “ether" and with the root word, kas, meaning “to be visible,” “sky,“ "atmosphere” or “open space.” It is used in traditional Indian cosmology and is also present in some examples of Western spiritualism.
In Hinduism, it is used to mean the essence of everything that exists in the material world. It is one of the five elements that make up the pancha mahabhuta, with the others being earth, fire, air and water.
Yogapedia explains Akasha
Akasha is still used in the literal sense of "sky," but the more exact philosophical meaning is “ethereal fluid imagined as pervading the cosmos.” It is also sometimes referred to as the imperceptible force that the rest of the world is derived from.
The main characteristic that is attributed to akasha is shabda (sound).
For Buddhists, akasha is split up into akasa-dhatu, which means "limited space," and ajatakasa, which refers to endless space.