Final answer:
An imaginary mass term represents a temporary violation of the conservation of mass-energy as allowed by the Heisenberg uncertainty principle. Virtual particles with imaginary mass can exist for a brief period of time.
Step-by-step explanation:
An imaginary mass term in a physical interpretation means that the particle associated with that imaginary mass is not stable and cannot exist as a real particle. It represents a temporary violation of the conservation of mass-energy as allowed by the Heisenberg uncertainty principle. Virtual particles with imaginary mass can exist for a brief period of time, according to the uncertainty principle, before they annihilate or transform into other particles.