When wavelength of the light is stretched enough to enter in the red part of the spectrum it is known as Redshift. Hubble discovered that light from the distant galaxies appeared to be stretched to longer wavelength or reddened also known as redshift.
Redshift proves that our universe is not only expanding in a certain direction but it is expanding in all the directions.
Blueshift is just opposite to redshift when wavelength of the light is decreased as a result of increase in frequency. In visible light color of the light shifts from red part of the spectrum to blue part.
It also means that source is moving towards the observer which is opposite to redshift where source and observer moves away from each other.
An observer moving away from a wave source will observe a change in frequency or wavelength due to the Doppler effect. In 1842, Austrian physicist Christian Doppler described the phenomenon.
You can observe the Doppler effect with sound waves, water waves, and electromagnetic waves, such as light or radio waves. People often observe this phenomenon in everyday life, such as the pitch change on a moving ambulance siren or the change in color of light as an object moves toward or away from them.
Waves appear to have a higher frequency when the source and the observer are approaching each other, and a lower frequency when they are moving apart as a result of the Doppler effect. As a result, the pitch or wavelength of a sound wave is perceived differently.
In radar technology, Doppler effect is used to measure the speed and distance of moving objects, while in medicine, Doppler effect is used to measure the flow of blood in the body.