Primary, Secondary, and Supplemental Characters

     So far as I understand it, the primary characters are your heroes, your viewpoint characters, those who undergo the major changes in the story.
     Secondary characters are involved in the minor story arcs that impact the plot, though they are not part of the main story and can be omitted from the synopsis. Secondary characters undergo no real changes to characterization. Quite frequently, secondary characters are the cannon fodder of the literary world.
     Then you have the supplemental characters, who are not part of any arc but are necessary to the story in some way, for background. The barmaid, the Innkeeper, the stable-hand. They do not impact the plot in any way, but are necessary to the atmosphere of the story details.