Short answers, pulled from the story.
A maritime boundary is a conceptual division of Earth's water surface areas using physiographical or geopolitical criteria. It generally bounds areas of exclusive national rights over mineral and biological resources. The conditions for establishing one are set out in the United Nations Convention on the Law of the Sea.
Maritime zones extend in concentric rings from a baseline. The territorial sea reaches 12 nautical miles, the contiguous zone reaches 24 nautical miles, and the Exclusive Economic Zone extends 200 nautical miles, except where two countries are less than 400 nautical miles apart.
Maritime boundaries divide ocean surface areas and govern rights over mineral and biological resources at sea. Lake and river boundaries are considered part of land boundaries and are not covered by maritime boundary terminology.
The United Nations Command unilaterally established a western line of military control between the two Koreas in 1953. North Korea rejects this line and has declared its own Military Demarcation Line, which is essentially a straight line, creating overlapping jurisdictional claims. Violent clashes in these waters include the first Yeonpyeong incident, the second Yeonpyeong incident, and the Bombardment of Yeonpyeong.
The Australia-France Marine Delimitation Agreement establishes ocean boundaries between Australia and New Caledonia in the Coral Sea, including the boundary between Norfolk Island and New Caledonia. It consists of 21 straight-line segments defined by 22 coordinate points forming a modified equidistant line, with its northernmost point forming a tripoint with the Solomon Islands.
Maritime boundary disputes are governed by customary international law and treaty law. Historic rights are evaluated through principles including acquisition, occupation, and rights that arose automatically from the beginning. Treaties on maritime boundaries serve as sources of international law, as evidence of existing customary law, and as evidence of developing custom.