The Cosmic Microwave Background (CMB) radiations are defined as one type of electromagnetic radiation which is generated after the big bang explosion. These are considered to be the remnant radio waves that are equally distributed in all the direction in space. These are not directly visible but their presence can be detected with the help of various detecting devices and instruments. One of the important significance of this wave is that it describes that the universe is constantly expanding.
Thus, these are the radio waves coming from distant galaxies.
