Resonance

The definition of Resonance is: Dictionary.com

1. The state or quality of being resonant.
2. The prolongation of sound by reflection; reverberation.
3. Phonetics.
   
   • amplification of the range of audibility of any source of speech sounds, especially of phonation, by various couplings of the cavities of the mouth, nose, sinuses, larynx, pharynx, and upper thorax, and, to some extent, by the skeletal structure of the head and upper chest.
   • the distribution of amplitudes among interrelated cavities in the head, chest, and throat that are characteristic for a particular speech sound and relatively independent of variations in pitch.
    
4. Physics.
   
   • The state of a system in which an abnormally large vibration is produced in response to an external stimulus, occurring when the frequency of the stimulus is the same, or nearly the same, as the natural vibration frequency of the system.
   • the vibration produced in such a state.
   • a hadron with a very short lifetime, of the order of 10 −23sec.
    
5. Electricity. that condition of a circuit with respect to a given frequency or the like in which the net reactance is zero and the current flow a maximum.
    
6. Also called mesomerism. Chemistry. the condition exhibited by a molecule when the actual arrangement of its valence electrons is intermediate between two or more arrangements having nearly the same energy, and the positions of the atomic nuclei are identical.
    
7. Medicine/Medical. (in percussing for diagnostic purposes) a sound produced when air is present.

 But, if you look further down the page:

Resonance   (rěz'ə-nəns)

  
Oscillation induced in a physical system when it is affected by another system that is itself oscillating at the right frequency. For example, a swing will swing to greater heights if each consecutive push on it is timed to be in rhythm with the initial swing. Radios are tuned to pick up one radio frequency rather than another using a resonant circuit that resonates strongly with the incoming signal at only a narrow band of frequencies. The soundboards of musical instruments, contrastingly, are designed to resonate with a large range of frequencies produced by the instrument. See also harmonic motion. 

Seems vague at most. Some hints, but no real definition. Perhaps the best words used are: Natural Vibration

Resonance is the most Efficient Way to bring about a Natural Vibration - Minimum Input and Maximum Output, the Maximum Q Factor achievable.

This does not always mean LC Resonance! There are many types of Resonance! Electron Spin Resonance is an example of another type of Resonance. Mechanical Resonance, Nikola Tesla's Earthquake Machine

So Resonance, is an art-form, the ability to break a glass with a singing voice:

*** I think it is really important to note: We want Electrons inside the Insulated Copper Wire to move, so we use Resonances, ESR, Wave Propagation, any other Resonance to efficiently make Electrons Move:

Floyd Sweet wrote:

Resonance frequencies may be maintained quite constant at high power levels so long as the load remains constant. We are all familiar with AM and FM propagation, where in the case as AM, the voltage amplitude varies, and with FM, the frequency is modulated.

However, the output power sees a constant load impedance, that of the matched antenna system. If this changes, the input to the antenna is mismatched, and standing waves are generated resulting in a loss of power. The frequency is a forced response and remains constant. Power is lost and efficiency becomes less and less, depending on the degree of mismatch.

NOTE: Antenna's are Current based Devices (Electric Field) - The Standing Wave mentioned in the above Video and Quote is a Standing Wave of Current, Not the Magnetic Field. Please don't confuse this Standing Wave with the Magnetic Standing Wave, Each are 90 Degrees from each other:

Also wrote about ESR:

Referring to the Jensen machine stated: natural magnetic resonance freq = 2.80GHz the nuclear magnetic resonance of a free electron when charges in magnetic states are induced by magnetic field the changes in states causes a condition called electron paramagnetic resonance, or EPR. The EPR of a free electron is 2.80 H MC. Where H is in gauss. This should be the initial state of the defining mathematical format.

I have been told, Wave propagation Theory is not Complete, it is not 100% Correct. But, it certainly has bought us a long way in the last Decades we have used it. Some of my friends disagree with my evidence here. So beware, there maybe some possible doors to be opened here.

 NOTE: This is only Part One of a Three Part Storey, we need to Use Electromagnetic Induction to complete the Storey!