This is a map of the entire universe, specifically of the cosmic microwave background radiation that formed as a remnant of the Big Bang. And the circled region is where the CMB is so cold that it defies easy explanation.
As a whole, the CMB is responsible for raising the overall temperature of the universe by about three degrees Celsius. But, while it's generally a fairly even distribution, some parts are warmer than others - you can see those in yellow and red - while others are far colder. It's these dark blue regions that have puzzled scientists:
How could part of the early universe be so cold? No one is sure, and many astronomers now think that the CMB Cold Spot on the cosmic microwave background (CMB) radiation is not particularly noteworthy. As the early universe expanded and cooled, it suddenly and predictably became transparent. The photons that come to us from that epoch are seen all around us as the CMB. Now this radiation field is quite uniform but does have slight warm and cool spots that tell us a great deal about the early universe that could have imprinted them. Except, possibly, one spot. This CMB Cold Spot, circled above on the WMAP 7-year all-sky map, has attracted attention as possibly being too large and too cold to be easily explained.
That hasn't stopped scientists from trying to explain it, even if the explanations are pretty out there:
Published speculation has included spectacular progenitor hypotheses that involve a supervoid, a cosmic texture, or even quantum entanglement with a parallel universe. Quite possibly, though, even a more mundane universe might be expected to show such a statistical peculiarity, and so explanations of the CMB Cold Spot like these might say more about human imagination than the early universe.
Yeah...but it's still awesome to talk about.