Junction, confluence, concourse are comparable when meaning the act, state, or place of meeting or uniting.
Junction, the most general of these words, applies to the meeting or uniting usually of material things (as roads, rivers, lines, or railroads) or less often of immaterial things and only occasionally of persons or groups of persons.
Confluence suggests a flowing movement that brings things together. It is applicable to two or more things or persons viewed as things which flow or seem to flow toward a point where they merge and mingle. It specifically applies to the place at which streams unite, often to form a larger stream or body of water.
Concourse places the emphasis on a running or flocking together of great numbers of persons or things. It is commonly used of a place, sometimes out of doors but sometimes in such a great building as a railroad terminal, in which there is an endless flow of persons or things passing through.