The statistical energy analysis is based on the expression for the power flow between coupled dynamic systems, each consisting of a multiplicity of modes. Usually, the expression is derived by properly identifying the modes as mechanical oscillators and by simply generalizing the expression for the power flow between two coupled mechanical oscillators. The latter expression states that the power flow is proportional to the difference in the “temperatures” of the two mechanical oscillators. In the generalization, cross‐modal terms are neglected and dismissed. In the presentation, the expression for the power flow between two multimodal dynamic systems that are coupled by a single link attached at localized positions on the dynamic systems is derived in full. The cross‐modal terms are identified and isolated. A number of conditions under which the cross‐modal terms tend to vanish so that they can be neglected are illustrated and discussed.