An interaction in which resources are exchanged without net gain or loss, though the participants individually may gain or lose. But the sum of all gains from the interaction must equal the sum of all losses. Newtonian mechanics are zero-sum in theory, though not in practice: the principle of conservation of overall energy (namely “the total energy of an isolated system must remain constant” suggests a zero-sum arrangement, but inevitably some kinetic energy in the system will be converted into thermal energy and lost to the system, so the kinetic energy in an isolated system will dissipate over time. The system will be “negative-sum” — it will need more energy injected to keep operating.
See also