Any membrane; specifically, one of the membranous coverings of the brain and spinal cord.
The brain and spinal cord are covered by 3 connective tissue layers collectively called the meninges that consist of the pia mater, the arachnoid and the dura mater. The meninges also support blood vessels and contain cerebrospinal fluid. Meningitis is an inflammation of the meninges; if severe, may become encephalitis, or inflammation of the brain.