Acording to Wikipedia:
Box models are simplified versions of complex systems, reducing them to boxes (or reservoirs) linked by fluxes. The boxes are assumed to be mixed homogeneously. Within a given box, the concentration of any chemical species is therefore uniform. However, the abundance of a species within a given box may vary as a function of time due to the input to (or loss from) the box or due to the production, consumption or decay of this species within the box.
Simple box models, i.e. box model with a small number of boxes whose properties (e.g. their volume) do not change with time, are often useful to derive analytical formulas describing the dynamics and steady-state abundance of a species. More complex box models are usually solved using numerical techniques.
Climate model: Box models, Wikipedia.
Slingerland and Kump, Mathematical Modeling of Earth’s Dynamical Systems - a Primer, Princeton University Press, Princeton, 2011.
J. L. Sarmiento and J. R. Toggweiler, A new model for the role of the oceans in determining atmospheric PCO2, Nature 308 (1984), 621–24. doi:10.1038/308621a0.
See also Climate model.