Administrative law regulates a myriad of aspects of social life, some of which are highly specialized. One example is investment trials, where a high level of specialization necessitates the use of precise language. It is against this background that legal definitions are emboldened in their role and importance. The article reviews of definitions in administrative law and concludes that they are neither sufficiently coherent nor accurate. Two groups of issues may be pointed to. First, in many instances the legislator, by treating a given definition as fundamental to a given fragment of social life, unwarrantedly broadens its systemic scope, a doubtful mechanism. Second, it is uncertain whether local administrative authorities are empowered to independently define concepts.