The animal unit has been a multiple-use concept in the natural resource sciences. This paper examines the animal unit as an example of a general process of concept design, a process involving multiple options for defining the concept, and multiple objectives and multiple applications for the concept in range management science. Based on this analysis, the animal unit is abstracted as a unit of energy demand independent of interactive considerations of forage or environment. The proposed definition optimizes the utility and universality of the concept by minimizing confounding in the concept's most important applications. The result is a simplified concept that can be used to explicitly express animal equivalences, and can be used in a web of more complex, interactive concepts and models involving human objectives, natural resources, and livestock. The animal unit and animal-unit equivalent are relatively simple examples of synthetic concepts involving communication that are central to the identity of range management science.