What is the meaning of Cerebrospinal_fluid?

A clear bodily fluid in the form of a very pure saline solution with microglia that occupies the subarachnoid space in the brain (between the skull and the cerebral cortex), and which acts as a cushion or buffer for the cortex.

A bodily fluid filling the third ventricle and surrounding the interthalamic adhesion.

Source: wiktionary.org