Grey Substance

The grey matter of the CNS comprises those parts which are composed of the cell bodiesn of the neurons.

You histological The opposite is white matter. It comprises the totality of all axon of the CNS. It is also known as Mark.

The grey substance on the surface of the brain is called cerebral cortex or cortex, deep grey areas surrounded by white substance, as nuclei or basal ganglia.

https://de.wikipedia.org/wiki/Graue_Substance _{(Wikipedia CC-by-sa-3.0)}