A more thorough explanation:

Definition: The navigable sea is a term used in international law to refer to the ocean waters that are divided into three zones of control among nations:

1. Inland waters: These are the waters near a nation's shores over which a nation has complete sovereignty.
2. Territorial waters: These are measured from the seaward edge of the inland waters, over which a nation has extensive control but over which innocent parties must be allowed to travel to other nations.
3. High seas: These are international waters not subject to the domain of any single nation.

For example, the United States has complete sovereignty over the waters within 12 nautical miles of its coastline, which are considered inland waters. However, innocent parties, such as foreign ships, are allowed to travel through these waters to reach other nations.

The navigable sea is an important concept in international law because it helps to define the rights and responsibilities of nations with respect to the use of ocean waters. By dividing the ocean into different zones of control, nations can regulate activities such as fishing, shipping, and resource exploration in a way that is consistent with their own interests and the interests of other nations.