 To model a phenomenon is to construct a formal theory that describes and explains it. In a closely related sense, you model a system or structure that you plan to build, by writing a description of it. These are very different senses of ‘model’ from that in model theory: the ‘model’ of the phenomenon or the system is not a structure but a theory, often in a formal language. The Universal Modeling Language, UML for short, is a formal language designed for just this purpose. It’s reported that the Australian Navy once hired a model theorist for a job ‘modelling hydrodynamic phenomena’. (Please don’t enlighten them!) 