Multiphysics refers to the study of systems and phenomena that involve multiple physical phenomena, such as the interaction of mechanical, thermal, electrical, and chemical effects. It is a broad field that encompasses a variety of disciplines, including engineering, physics, biology and chemistry.

In a Multiphysics problem, the behavior of a system is determined by the interplay of multiple physical phenomena, and understanding the system requires taking into account the interactions between these phenomena. For example, in the design of a fuel cell, the electrical and chemical properties of the materials used, the temperature and pressure of the system, and the mechanical stresses on the cell all need to be considered in order to understand and optimize the performance of the fuel cell.