grey matter

https://doi.org/10.1351/goldbook.10781

Regions of the brain and spinal cord that are made up primarily of cell bodies and dendrites of nerve cells rather than of myelinated axons.

Compare: white matter
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 762 [Terms] [Paper]