What defines a junction in nautical terms?

In nautical terms, a junction is typically defined as a point where two channels merge into one. This definition is particularly important for navigation, as it indicates where boats must choose to either continue in the existing channel or enter into another. The specific definition focused on "two channels into one when going out to sea" highlights the transitional nature of navigation in coastal areas where vessels may be departing from a confined waterway and heading towards the open sea. Navigation at such points requires attention to depths, currents, and the course of other vessels, making the understanding of junctions critical for safe passage.

The focus here is on the merger aspect which signifies the flowing together of navigable routes. The other options generally describe different scenarios related to navigation but do not encapsulate the precise meaning of a junction as effectively as the correct answer does. Other aspects of channels, such as separation or longer routes, do not define a junction in the context of merging routes necessary for safe sea navigation.