Not to be confused with the characters whom SpongeBob and Incidental A18 respectively call "secondary characters" in Jimmy Neutron's Nicktoon Blast[1] and The Crossover Time Movie: Heroes on the Water[2].
The "secondary characters" are one of the types of regular incidental characters. They appear to be for incidentals who usually play more supporting roles than most other incidentals who usually play minor roles or usually appear in the background. Most of these characters also tend to regularly be portrayed as a character with an occupation. There are currently a total of 14 incidental characters.
