cosmic background radiation - (n.)
The primordial radiation field that fills the universe. It was created in the form of gamma rays at the time of the big bang, but has since cooled so that today its temperature is 3 K and its peak wavelength is near 1.1 millimeters (in the microwave portion of the spectrum). Also known as the 3-degree background radiation. Also called cosmic microwave background radiation, CMBR.