Myelin is a fatty, insulating substance that surrounds nerve fibers and speeds up the transmission of nerve impulses. There are several synonyms for myelin, including neurilemma, neurolemma, medullary sheath, and white matter. Neurilemma and neurolemma are both used to describe the outermost layer of Schwann cells that encase peripheral nerve fibers. The medullary sheath refers to the fatty layer of myelin that surrounds nerve fibers within the central nervous system. White matter is another term for the myelinated nerve fibers within the brain and spinal cord that are responsible for communication between different parts of the nervous system. Understanding these synonyms can help improve scientific communication in the field of neuroscience.