It was originally a trade name for naphthalene, which takes its name from naphtha ("hydrocarbon") as the "coal tar" from which it comes and so it is also known as "white tar". Today it is a generic name for naphthalene compound pills that are used as a disinfectant and repellent for moths and other insects that feed on woolen tissues and the like. Figuratively it is associated with old things, kept for a long time and that have the characteristic aroma of naphthalene so they were protected from pests. See acaroine.
