Light is just one portion of the various electromagnetic waves flying through space. The electromagnetic spectrum covers an extremely broad range, from electrical and radio waves to gamma rays. The visible light region is only a very small portion of this: from 380nm to 780nm.

If we pass light from the sun through a prism, we create a color distribution called a visible spectrum. This phenomenon was discovered by Issac Newton.

The reason that the human eye can see the spectrum is those specific wavelengths stimulate the retina in the human eye.