Resonance in Wind Instruments

Question:

How does resonance in wind instruments work to make its sounds? What is overtune?

Answer:

The energy imparted by the musician's breath causes either her lips or a reed, or a slot to vibrate in a complicated way which includes many frequencies. By altering the physical characteristics of the instrument by opening of closing ports or valves one, or a range, of the available frequencies are amplified through resonance because the energy being reflected back to the oscillator is in phase at the chosen frequencies.

I am not familiar with the term overtune. It sounds like it might have to do with the broadening of the band of selected frequencies by a slight mismatch between the frequencies of the driving source and the resonance of the chamber.

Regards,

JDJ