I can't/don't know how to make it in me own words but here's the definition
In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, river delta or strait. The word is cognate to canal, and sometimes shows in this form, e.g. the Hood Canal. Most examples of this are fjords in the Pacific Northwest; a notable exception is the Casiquiare canal. All likely share borrowing from Spanish, Portuguese or French.