Ākāśa is the element of space, in which all things exist and through which sound travels. The Upaniṣads use it as an image of Brahman, all-pervading and untouched by what it contains, and of the space within the heart where the self is found.
Ākāśa
Space or ether: the first and subtlest of the five elements, whose quality is sound.
Also: Akasha, ether