Definition of Vijnanamaya kosha:
Vigyanamaya Kosha is the fourth of the five koshas that cover the Atman. Vigyanamaya Kosha literally means a shell that is made up of wisdom.
It is also the first layer of the causal mind located at the Vishudda chakra, the Ajna chakra, and the Sahasrara chakra. Metaphysically, it is considered the first incarnation of light.