It's often used in medical terms to refer to something related to the gray matter of the brain or spinal cord, which is where the nerve cells are located.
For example:
* Poliomyelitis (also known as polio): A viral disease that affects the gray matter of the spinal cord, leading to paralysis.
* Poliencephalitis: Inflammation of the gray matter of the brain.
So, the prefix "polio-" essentially refers to something that affects or is related to the gray matter of the nervous system.