A major component of the central nervous system, consisting of nerve cell bodies.
Grey matter refers to the darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and branching dendrites. It includes parts of the brain involved in muscle control, sensory perception and decision making. White matter is the paler tissue of the brain and spinal cord made up mostly of impulse-conducting axons (the nerve fibres that carry messages around the body).
References:
The Human Memory. Gray and White Matter: Structure and Functions. Available at: https://human-memory.net/gray-white-matter/. Accessed May 2020.