User blog comment:BlueBarracudaMary/Protagonist, Deuteragonist, Tritagonist, Tetartagonist, Pentagonist, What Comes Next?/@comment-32814654-20180428003605/@comment-961279-20200131154330

It's a made-up word for a character so unimportant in the story that you probably won't notice them in a crowd. One of the background characters whose purpose likely is to only as space-filler in a scene.