Akasha is a sanskrit word meaning, "subtlest ether, inner space." It is one of the five great elements in Hinduism.
Akasha is best understood as living inner space - alive emptiness. Almost pure bliss consciousness itself. Our body is that - energy in vast empty space. There is nothing much here. Only the appearance of something. Akasha means that.
Read about using akasha and samyama here: Samyama practice, and the two lessons that follow it.