Final answer:
Cerebrospinal fluid (CSF) is the fluid in the brain that is free flowing between the brain parenchyma, CSF in ventricles, and subarachnoid space. It acts as a cushion and provides mechanical and immunological protection to the brain.
Step-by-step explanation:
The fluid in the brain that is free flowing between the brain parenchyma, CSF in ventricles, and subarachnoid space is cerebrospinal fluid (CSF).
CSF is a clear bodily fluid that occupies the space between the arachnoid mater and the pia mater, as well as the ventricles, cisterns, and sulci inside the brain. It acts as a cushion and provides mechanical and immunological protection to the brain.