Throughout history, banking has been key to the development of fundamental institutions and structures of capitalism, while also having been instrumental in its recurrent crises. However, this significance isn’t reflected in its definitions. In this brief note, I present a critical definition of banking institutions that takes into account their importance, as it approaches banking from a variety of perspectives. It conceives the bank as a mercantile-rentier that overlays social inefficiencies in monetary allocation through the transmission of internally-produced fungible rights in personam.