The frequency at which a system typically oscillates in the absence of any driving or damping forces is referred to as the natural frequency or eigenfrequency.
The resonant frequency is the frequency at which an external force causes an oscillating system to move with the greatest amount of motion (near to the system's natural frequency).
The frequency at which the system tends to oscillate in the absence of any driving or damping force is called Natural frequency.
For Example, a tuning fork is designed to vibrate at a particular natural frequency.
The frequency object appears to vibrate it is hit, plucked is the known object's normal frequency.
The fundamental frequency is the very first natural frequency in the line.