Possible sources of this phenomenon are identified by intersections on a Campbell diagram. “Tongues” of this phenomenon may be found with the Mathieu equation when considering its “parametric” form. A “universal” curve for this phenomenon is quantified by the half bandwidth of a Lorentzian function. Injection locking may cause the “sympathetic” form of this phenomenon. This phenomenon occurs more intensely but in a more narrow region when the Q-factor is high, (10[1])corresponding (-5[1])to underdamped (10[1])systems (-5[1])with little energy loss. This phenomenon is typically distinguished from the self-exciting aeroelastic flutter that caused the collapse of the Tacoma Narrows Bridge. (10[1])For 10 points, (10[1])name this phenomenon in which an oscillator driven at its natural frequency grows (10[1])in amplitude. (10[1])■END■