Cerebrospinal fluid (csf) is a clear, colorless transcellular body fluid found within the meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricles of the brain. The meaning of cerebrospinal is of or relating to the brain and spinal cord or to these together with the cranial and spinal nerves that innervate voluntary muscles. Cerebrospinal fluid (csf) is a clear, colorless bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord.