Redshift is a physical concept which describes a shift in the light spectrum towards the red part of the spectrum which is emitted by distant galaxies. Based on this phenomenon the Hubble Law was concluded which states that the velocity at which the galaxies receded were proportional to the distance and that the redshift increased with the distance.
Detailed Definition:
This phenomenon was described as an effect of the Doppler shift when it was first discovered by Hubble.
The Doppler shift is a effect where an observer which moves away from a light source can see light with a longer wavelength than the emitted light (redshift). If the observer moves towards the light source the light appears to have a shorter wavelength (blueshift).
A characteristic of the universe which was concluded by Edwin Hubble by the redshift is that the Universe is expanding.
The previously mentioned Hubble Law is the following cosmological velocity-distance law in a equation: velocity = Ho x distance. The variable Ho is the Hubble constant, which describes how fast the universe is expanding and isn´t yet measured.
