Lumped-Element Model
An approximation in which a circuit is represented by idealized components and terminal variables rather than by solving distributed electromagnetic fields everywhere.
Solving the electromagnetic field at every point in a circuit is unnecessary for many circuit problems. The lumped-element model treats resistors, capacitors, inductors, and similar components as idealized elements whose electrical behavior is described through terminal voltages and currents.
The approximation is most useful when the physical dimensions of the circuit are sufficiently small relative to the electromagnetic wavelength associated with the signals of interest. Once propagation delay, transmission-line behavior, or distributed parasitics become significant, a purely lumped description can cease to be adequate.
A lumped model is therefore not a claim about the exact physical structure of a circuit. It is a scale-dependent engineering abstraction.
Related lecture note: Circuit Theory.