What is the definition of resonance?

In physics, resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies.

In music, resonance is the characteristic of sound waves vibrating in either the open air or within an enclosed structure, which can include a musical instrument. Like in a violin, when the strings are bowed, the sound resonates within the box (the hollow part of the instrument) and thus becomes a bit more amplified for us to hear.

The Link below gives a simple and lively explanation of the concept of resonance.

http://analog-design-for-chickenbrain.blogspot.com/2009/05/what-heck-is-resonance.html