"Underdamped" refers to a condition in a dynamic system where oscillations occur but gradually decrease in amplitude over time. This behavior is often observed in systems like mass-spring setups or electrical circuits when the damping force is not strong enough to prevent oscillations entirely. In an underdamped system, the oscillations can continue for several cycles before settling down to a stable state. This is characterized by a quick return to equilibrium, but with noticeable oscillations that diminish slowly. Understanding underdamped systems is crucial in fields like mechanical engineering and control systems.