Not to be confused with undampned, undampened describes a mechanical system without losses (such as friction, or drag through air). The most common example is a bell ringing or your Great Aunt Pearl's '67 Plymouth Fury wagon when it blew a shock abosrber. No systems are truely undampened as there's always some losses in bearings or in the transfer of vibrations to the air to make sound etc. Such systems are extremely vulnerable to resonance. You know what resonsance is, you knew it when you were 4. Resonance is adding energy to a system at the right frequency, creating a strong frequency response: swinging your legs and shifting your weight on a swing.