Natural Frequency: This is the frequency of vibration of a system that is undamped and without external excitation while it is disturbed.

Forced Vibration: This is the vibration of a system that is because of external excitation.

Reference : While forcing frequency is equivalent to the natural frequency, resonance occurs.

Degree of Freedom: This is equivalent to the number of independent coordinates that are needed to define the motion of the system.

Mode of Vibration: This is the way, the system vibrates in the free vibrations.

Conservative System: This is the system for which entire energy remains constant.

Damper: This is the element that is responsible for decay in energy.