The change in frequency of a wave in relation to an observer who is moving relative to the wave source is known as doppler effect.
The increment in the wavelength and decrement in the frequency and photon energy is known as redshift.
While blue shift is opposite to red shift as it is the decrement in the wavelength and increment in the frequency and photon energy.
As we know that the Doppler Effect can be illustrated through redshift. As an item travels away from us, the sound or light waves it generates are stretched out, resulting in a lower pitch and a shift to the red end of the electromagnetic spectrum, where light has a longer wavelength.
The terms redshift and blueshift explain how the frequency of a light wave changes based on whether an object is travelling towards or away from us.
A redshift in physics is a rise in the wavelength of electromagnetic radiation with a matching drop in frequency and photon energy (such as light).
A negative redshift also referred to as a blueshift, is a shift in which the wavelength decreases while the frequency and energy increase simultaneously.
The light emitted as an object moves away from us is known as redshift; when an object moves towards us, the light emitted is known as blueshift.
In the following figure Arrows show redshift approaching the red and beyond, the wavelength lengthens (frequency decreases).