Explain what is meant by red - shifted

The red-shift is the phenomena of the electromagnetic radiation that are emitted from a source that undergoes an increase in wavelength according to the observer.

Explanation:

The red-shift is considered as the Doppler effect in the electromagnetic radiation.It is similar to the phenomena of sound waves in the Doppler effect, where the perceived frequency of the electromagnetic radiation emitted by a source tends to increase its wavelength with respect to the observer.The red-shift occurs when both, the source and the observer are receding each other.If a spectrum of the star or galaxy is red-shifted, it means they are receding from us.So, when there is an increase in the wavelength of the emitted spectrum of radiation from the source. It is meant that the source is red-shifted.