0D – point: A background character with no lines, or none that couldn't be said by absolutely anyone else in the world.
Example: An old man in the background who never speaks and is essentially scenery. If the main character bumps into him, he says “Ouch” and never shows up again.
1D – line: A character with one defining trait and nothing beyond that. They're typically joke and/or background characters, but occasionally characters will be played completely straight as “good” or “evil” and nothing more.
Example: “I'm old!” - The main character bumps into an old man who responds by saying, “Watch where you're going, young whippersnapper.” he then shows up every so often throughout the hero's adventure to say similarly “old” things.
2D – plane: A character who perfectly fits an archetype with set traits and role. You know everything about this character when you see them.
Example: “I'm old and wise and here to guide you.” - He helps the hero on his journey with ambiguous advice and “ice cream koans” and dies when things get serious.
2.5D: They generally comply to an archetype, but with a twist. It gives the illusion of depth and can get very close to being three dimensional, but doesn't quite reach the level of being a complex, fully fleshed out person.
Or; a character whose characterization jumps around as the plot demands. They appear three-dimensional at times, but each time they show up they've changed completely with no real reason given. Their personality usually alternates between two- and three-dimensional.
Example: “I'm and old and wise woman who is here to guide you. Sometimes I want to guide you off a cliff and sometimes I don't, I don't know why and nor does the audience.”
3D – space: A deep, complex character who is based more on motivations than set traits. They are like a real person and make sense in that way.
Example: “I'm old and wise and might be guiding you off a cliff.” - She's so helpful because she's actually guiding the protagonist off a cliff out of a misguided desire for revenge because they caused the death of her child.
4D – time: A fully fleshed out, realistic character that changes over time in a realistic way – not just because the plot says so.
Example: “I was going to guide you off a cliff, but then our journey together changed my heart” - The wise, old mentor was going to kill the protagonist, but after helping them along their way and becoming attached to them, she was overwhelmed by her morals and had a change of heart and decided to help them in earnest instead.
5D – spacetime???: A fully fleshed out character whose perspective is interwoven into the story itself. The audience sees how they view their world and how they effect it because of said perspective. They have more than just traits and motives, but full trains of thought as well.
Example: “I'm old, wise, conflicted and may or may not be guiding you off a cliff - and the audience will get to listen to me think about it for the next several pages.” The audience gets to hear the old mentor's reasoning as she goes from wanting to kill the protagonist, to giving up her quest for vengeance.