What is Sustained Oscillations?

Hint: The system is in charge of controlling forces from outside the system. Sustained Oscillation maintains a system's periodic oscillation at a period or frequency that is close to the system's natural period.

Complete answer:
Sustained oscillation is a sort of oscillation in which each cycle is exactly the same as the one before it. Sustained oscillation in control theory refers to oscillation that continues due to a lack of attenuation in the feedback route. Sustained oscillation is defined in physics as oscillation in which forces external to the system, yet controlled by it, maintain a periodic oscillation of the system at a period or frequency that is close to the system's natural period.
Sustained-oscillation is defined as the development and maintenance of a periodic motion by a power source with no corresponding periodicity. The phase with which external power works on the oscillator is controlled by the oscillator itself. Forced and parametric resonators, in which the power that supports the motion must be regulated externally, are so distinct from self-oscillators.
Sustained-oscillation emerges in linear systems as an instability with a negative damping term, causing tiny disturbances to expand exponentially in magnitude. A positive feedback between the oscillation and the modification of the external source of power causes this negative damping. The nonlinear features of the system determine the amplitude and waveform of steady self-oscillations.
The same phenomenon is sometimes labelled as "maintained", "self-exciting", "self-induced", "spontaneous", or "autonomous" oscillation.

Note:
One of the conditions for maintaining oscillations in an Oscillator is regenerative or positive feedback. To make a functional Oscillator circuit, this feedback can be used in a variety of ways. An oscillatory circuit is one that generates electrical oscillations at any specified frequency.