Resonance effect for various input frequencies and damping coefficients

In physics, resonance is the tendency of a system to vibrate with increasing amplitudes at some frequencies of excitation. These are known as the system's resonant frequencies (or resonance frequencies). The resonator may have a fundamental frequency, and any number of harmonics.

An example of useful effect of resonant frequency is a guitar string which makes a characteristic noise when it is touched. The noise depends on how thick or slack the string is.