The definiteness principle of the law comprises three main requirements, i.e. clarity, precision and explicitness. A significant factor, which under certain communication circumstances may be used to meet these standards, is the legal definition. This article determines when it is particularly necessary to include a definition and considers situations in which doing so is not justified. Legislation is the context for those considerations. Under certain circumstances, even in socially significant areas, defining particular, previously undisputed terms seems redundant. This concerns, for instance, defining the “X” sign on a ballot paper. The author contends that although a definition has the potential to become a valuable instrument of proper legislation, poorly formulated definitions may just as well impede proper legislation.