The cold spot (or CMB cold spot or WMAP cold spot) is
a region of the celestial sphere (a few tens of square degrees)
in which the cosmic microwave background (CMB) indicates a slightly lower temperature
than the rest, a difference on the order of 70 millionths of a kelvin.
The temperatures indicated by the CMB's black-body spectrum
across all the different portions of the celestial sphere generally
form a tight Gaussian distribution (a type of random distribution)
around a specific value, about 2.72548 K. However, at least one
test of gaussianity indicates this region's temperature is anomalously
low, suggesting it is an unlikely characteristic if there is a
physical reason for the randomness seen across the whole sky.
There has been some investigation regarding whether the apparent
colder region corresponds to a void or voids in that direction,
showing the low temperature due to a Sachs-Wolfe effect.