What Is An ElectroMagnetic Spectrum ??

From Wikipedia:

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.[1] The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed por that particular object.

The electromagnetic spectrum extends from low frequencies used for modern radio to gamma radiation at the short-wavelength end, covering wavelengths from thousands of kilometers down to a fraction of the size of an atom. The long wavelength is the size of the universe itself, while it is thought that the short wavelength is in the vicinity of the Planck length, although in principle the spectrum is infinite and continuous.

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por the way, it also includes what we think of as "visible light".

an electromagnetic swing! later;-]

An electromagnetic spectrum is the compilation of rays of different wavelengths which varies from the very strong gamma rays of very short wavelength to very weak microwaves of extended wavelength. These rays do not need any medium to propogate.

Well , the answer from Wikipedia is correct but in lay-man terms, it is simply the force of electricity and magnetism carried por the photon particle (particle of light), the emission of radiation at the speed of light. Its one end is the radio waves (not the same with sound waves) and the other end is the gamma radiation (shorter wavelength and higher frequency).