Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Territorial waters \Ter`ri*to"ri*al wa"ters\ (Internat. Law) The waters under the territorial jurisdiction of a state; specif., the belt (often called the
marine belt or
territorial sea) of sea subject to such jurisdiction, and subject only to the right of innocent passage by the vessels of other states.
Perhaps it may be said without impropriety that a
state has theoretically the right to extend its
territorial waters from time to time at its will
with the increased range of guns. Whether it would
in practice be judicious to do so . . . is a widely
different matter . . . . In any case the custom of
regulating a line three miles from land as defining
the boundary of marginal territorial waters is so
far fixed that a state must be supposed to accept it
in absence of express notice.
--W. E. Hall.
Wiktionary
n. (context politics geography English) A country's inland lakes and waterways as well as the portion of its coastal oceans, seas, or other adjoining body of water considered to fall within the political boundaries and legal jurisdiction of that country.
WordNet
Wikipedia
Territorial waters or a territorial sea as defined by the 1982 United Nations Convention on the Law of the Sea, is a belt of coastal waters extending at most from the baseline (usually the mean low-water mark) of a coastal state. The territorial sea is regarded as the sovereign territory of the state, although foreign ships (both military and civilian) are allowed innocent passage through it, or transit passage for straits; this sovereignty also extends to the airspace over and seabed below. Adjustment of these boundaries is called, in international law, maritime delimitation.
The term "territorial waters" is also sometimes used informally to refer to any area of water over which a state has jurisdiction, including internal waters, the contiguous zone, the exclusive economic zone and potentially the continental shelf.