Unwanted oscillations that can occur in amplifier or oscillator circuits. The frequency of such oscillations is usually very much higher than the frequencies for which the circuit has been designed since it is mainly determined by stray inductances and capacitances, such as in connecting leads, and by interelectrode capacitances.

Parasitic stoppers are devices incorporated into a circuit to prevent parasitic oscillations being generated. They are commonly resistors used in the input and output circuits of the device. They take their name from the particular part of the circuit in which they are incorporated. For example, an anode stopper is connected to an anode, a grid stopper to a grid, and a base stopper to a base.