Editor's Note: This is the first installment in a series of primers produced in partnership with the Center for International Maritime Security (CIMSEC).

“Words have meanings.” It’s easy to dismiss this statement as a truism. But words – and their meanings – do hold particular import in the multi-layered realm of maritime territorial disputes, where the distinction between a rock and an island can mean the difference between hundreds of square miles of Exclusive Economic Zone. At times, usage of words has itself opened new fronts in conflicts, as nationalist fights over names of bodies of waters in textbooks have shown. Those wishing to understand and accurately describe maritime Asia’s long-standing territorial disputes must wade through a colorful and evolving vocabulary. So, in an effort to help bring clarity to the lexicon we offer this guide to common terms in use.

U.N. Convention on the Law of the Sea (UNCLOS): UNCLOS is the international agreement that resulted from the Third UN Conference on the Law of the Sea from 1973-1982. It establishes the maritime zones that divide the modern seas, and the rights and sovereignty of states within them. It also provides means for determining sovereignty within disputed areas. The United States has neither signed nor ratified UNCLOS but regards all but several clauses relating to the International Seabed Authority as customary international law that it therefore follows. Several additional key international terms below are defined in UNCLOS. A full reading of the Convention is highly recommended for any serious student of international affairs to gain a better appreciation of the nuances of the terms than can be spelled out here:

Territorial Waters: Extends 12 nautical miles (nm) from a country’s internationally agreed upon baseline. A coastal state has full sovereignty over its territorial waters, but other states’ vessels (including military, but not aircraft) enjoy the Right of Innocent Passage through these waters so long as their passage is “continuous and expeditious,” and not “prejudicial to the peace, good order or security of the coastal State.” For example naval vessels cannot engage in spying during the transit and submarines must transit surfaced. A similar concept is that of Transit Passage, enabling the “continuous and expeditious” passage of all ships and aircraft through most international straits, as well as archipelagic states’ sea-lane passages (straits formed by two islands of the same state).

Contiguous Zone: Extends from 12nm out to 24nm from a country’s baseline. Coastal states’ rights here are limited to “customs, fiscal, immigration [and] sanitary laws and regulations.”

Exclusive Economic Zone (EEZ): Extends 200 nm out from the baseline, wherein a state enjoys exclusive rights to natural resources such as fish and oil. States may also enjoy some resource exploitation rights in the seabed and subsoil beyond the EEZ depending on the lay of the Continental Shelf.

In ratifying UNCLOS, China made a number of qualifying statements, the first of which read, in part: “the People's Republic of China shall enjoy sovereign rights and jurisdiction over an exclusive economic zone of 200 nautical miles and the continental shelf.” According to Bernard Cole, only fifteen of the 192 UNCLOS signatories take the same position as China on this issue.

Artificial Islands: Within its EEZ, a state has the “exclusive right to construct and to authorize and regulate the construction, operation and use of” artificial islands. However, “Artificial islands, installations and structures do not possess the status of islands. They have no territorial sea of their own, and their presence does not affect the delimitation of the territorial sea, the exclusive economic zone or the continental shelf.” Artificial islands have come to prominence in recent months due to China’s extensive reclamation projects in the South China Sea.

High Seas: Anything beyond a state’s EEZ. “No State may validly purport to subject any part of the high seas to its sovereignty.” The high seas are sometimes also referred to synonymously as International Waters, but this latter term is not well defined as it can also be used for everything outside a nation’s territorial waters. Note: Per UNCLOS, Piracy can technically occur only on the high seas or “in a place outside the jurisdiction of any state,” such as the waters of a failed state. This is why reporting of piracy statistics can be inaccurate unless it uses the term Piracy and Armed Robbery to capture piracy occurring within a nation’s EEZ.

The Freedom of Navigation: The overarching right of ships (and aircraft with Freedom of Overflight) to transit the sea unimpeded except as restricted by international law. Some states, such as China, claim rights not afforded to it by UNCLOS or customary international law, namely the ability to restrict activities of military assets and aircraft not inbound within its contiguous zone and EEZ (see for example the recent dispute over the right of U.S. P-8 Poseidon aircraft to fly outside of its territorial waters).

The United States conducts Freedom of Navigation operations to register its non-concurrence with China’s position on territorial rights, thereby preventing it from becoming accepted customary international law.

ITLOS (International Tribunal for the Law of the Sea): Established by UNCLOS to help settle maritime dispute. Its mandate is to “adjudicate disputes arising out of the interpretation and application of the Convention.” In 2013, the Philippines submitted a case to the ITLOS seeking a ruling declaring China’s Nine-Dash Line not in accordance with UNCLOS (and therefore not a valid basis for its South China Sea claims). The president of the ITLOS appointed an Arbitral Tribunal at the Permanent Court of Arbitration in The Hague to hear the case, and it is expected to make its ruling in the next two years. For its part, China is not taking part in the proceedings and has indicated it will not abide by the ruling. At the end of last year Vietnam surprised many by submitting a position paper to the court arguing that the Line is “without legal basis,” and asking that its rights and interests be considered in the ruling, but it is itself not a party to (has not “joined”) the case against China.

Air Defense Identification Zone (ADIZ): An ADIZ is not covered by any international agreement (and therefore there is no one definition) and does not confer any sovereignty over airspace or water, but has arguably become a part of customary international law due to its growing usage and acceptance. Foreign Affairs defined an ADIZ as “a publicly defined area extending beyond national territory in which unidentified aircraft are liable to be interrogated and, if necessary, intercepted for identification before they cross into sovereign airspace.” The rules China stipulated with its establishment of an ADIZ in the East China Sea in late 2013, however, garnered widespread criticism and non-observation due to its surprise announcement and application to those flights not intending to enter sovereign airspace.

Conduct for Unplanned Encounters at Sea (CUES): CUES provides a set of non-binding “ safety procedures, a basic communication plan and basic maneuvering instructions ” when naval vessels and aircraft unexpectedly encounter each other at sea. It was agreed upon at the 14th Western Pacific Naval Symposium in April 2014, and while a code of conduct, CUES should not be confused with the much-discussed and as yet elusive ASEAN Code of Conduct below. CUES was followed up in November 2014 at a summit between Presidents Xi and Obama with the U.S.-China Memorandum of Understanding (MOU) On the Rules of Behavior for the Safety of Air and Maritime Encounters. The MOU provides technical specifics and expected behavior for interactions between the two nations’ forces as spelled out in an annex on ship-to-ship encounters, with an air-to-air annex to come in 2015, although leaving the differing interpretations of permissible activities within a nation’s EEZ intentionally unresolved.

Code of Conduct (CoC): In 2002, the ASEAN member states and China signed a voluntary Declaration on the Conduct (DoC) of parties in the South China Sea “to resolve their territorial and jurisdictional disputes by peaceful means, without resorting to the threat or use of force, through friendly consultations and negotiations by sovereign states directly concerned.”

This was to be the precursor to a binding CoC, but as Carl Thayer ably documents implementation of the CoC was kept in check for a decade by China and focus on Guidelines to Implement the DoC, which were approved in 2012. However, promises in the DoC such as to refrain from then uninhabited maritime features and to handle differences in a constructive manner have since been violated by actions including several parties’ ongoing construction and expansion on features under their control.

As a result of this and because the Guidelines have been removed as the focus by adoption, many ASEAN states, with the Philippines foremost among them, have returned attention to concluding a legally binding CoC. There have been recent indications that China may be willing to soon start serious discussions about the Code of Conduct, but it is unclear whether it will be willing to accede to (let alone adhere to) any potent enforcement mechanisms.

Scott Cheney-Peters is a surface warfare officer in the U.S. Navy Reserve and the former editor of Surface Warfare magazine. He is the founder and president of the Center for International Maritime Security (CIMSEC), a graduate of Georgetown University and the U.S. Naval War College, and a member of the Truman National Security Project’s Defense Council.