1. The fluid in the space between the membranous and bony labyrinths of the inner ear.
2. The fluid which surrounds the membranous labyrinth of the internal ear, and separates it from the walls of the chambers in which the labyrinth lies.
3. The fluid contained within the osseus labyrinth, surrounding and protecting the membranous labyrinth.

Perilymph resembles extracellular fluid in composition (sodium salts are the predominate positive electrolyte) and, via the perilymphatic duct, is in continuity with cerebrospinal fluid.