It's interesting that a concept (including the examples here) is distinct from the plot (protagonist's quest and obstacles), the arc (protagonist's need), or the story's theme. In a way, concept permeates all of these elements. If plot, arc, and theme are what happens to the characters, concept is what happens in the audience (it's closer to the tagline than to the logline).

Aside: Chasing Amy has a "higher" concept than Clerks, (What if a man falls in love with a lesbian) but Clerks (for me as a viewer) is a more interesting story. (Maybe the concept of Chasing Amy helped Kevin Smith sell the script--I don't know the details of how he marketed it).