Free oscillations are defined as the oscillations of a particle with fundamental frequency under the effect of restoring force. Oscillations have a consistent amplitude, frequency, and energy. Free oscillation is an oscillator that keeps oscillating with a constant amplitude for an endless period of time.

B. Damped oscillations: Damped oscillations are defined as oscillations of a body whose amplitude decreases with time. Due to damping factors such as frictional and viscous forces, the amplitude of these oscillations reduces exponentially.

C. Forced oscillation: Forced oscillation is a type of oscillation in which the body oscillates under the effect of an external periodic force (driver). The driven body oscillates with the frequency of the driver rather than its own inherent frequency. The oscillator's amplitude lowers due to damping force, but it remains constant due to the energy acquired from the external source (driver). The difference between the applied force frequency and the natural frequency determines the amplitude of forced vibration.

D. Resonance: This state of driven and driven is known as resonance when the frequency of the external force (driver) equals the natural frequency of the oscillator (driven). The highest amount of energy is transferred from the driven to the driver when the system is in resonance. As a result, the motion's amplitude reaches its maximum.

The resonant frequency is the frequency at which the driver is in resonance.

E. Coupled oscillation: A coupled oscillation is a system of two or more oscillations that are linked together in such a way that they exchange energy. Coupled oscillations are the oscillations of such a system. The following are some instances of connected systems:

Three springs connect two masses that are held together by two rigid supports. The intermediate spring can be thought of as a link between the driven and driving systems.

Two simple pendulums are suspended from the same rigid support, their bobs connected by a spring.