An exclusive economic zone (EEZ) is a sea zone prescribed by the United Nations Convention on the Law of the Sea over which a state has special rights regarding the exploration and use of marine resources, including energy production from water and wind. It stretches from the baseline out to 200 nautical miles (nmi) from its coast. In colloquial usage, the term may include the continental shelf. The term does not include either the territorial sea or the continental shelf beyond the 200 nmi limit. The difference between the territorial sea and the exclusive economic zone is that the first confers full sovereignty over the waters, whereas the second is merely a "sovereign right" which refers to the coastal state's rights below the surface of the sea. The surface waters, as can be seen in the map, are international waters.
Within the MSP Challenge Game the EEZ indicates the Planning Region of a team. Planning outside of your team's EEZ requires the team who's border is crossed to approve the plan before implementation.
Adapted from http://www.marineregions.org/downloads.php#iceser
The dataset from http://www.marineregions.org/downloads.php#iceser combines the boundaries of the world countries and the Exclusive Economic Zones of the world. It was created by combining the ESRI world country database and the EEZ V7 dataset.