noun - A channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.
A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water. It is also a dredged and marked lane of safe travel which a cognizant governmental entity guarantees to have a minimum depth across its specified minimum width to all vessels transiting a body of water.
In a larger nautical context, as a geographical place name, the term channel is another word for strait, which is defined as a relatively narrow open body of water that connects two larger bodies of water. In this nautical context, the terms Strait, channel, Sound, and Passage are synonymous and usually interchangeable. For example, in an archipelago, the water between islands is typically called a channel or Passage.