So, I'm not an expert here, but lately I've been shown a lot of character drawings and asked if they are "character designs." I've been asked if sketches are character designs, or if the pieces need to be finished. I've been asked to what level the finish needs to be.
I'm not a character designer, but I've talked to a whole bunch, and obviously, I do have thoughts.
Essentially - No character image, no matter how finished, is a character design unless it fits into something bigger....and no character design is good if it fits into something bigger but you can't tell that from looking at it.
To me, those are your two thresholds.
1: Does it solve a problem or answer a question about a larger thing?
2: If it does, is that obvious from looking at it?
This applies to environments, vehicles, props, and all the other "concept art" you will ever see, but it is especially crucial in characters.
How finished does it need to be? There is no answer to that. It needs to be finished enough to answer any questions that arise from the person who is going to integrate it into the larger whole. If *you* are the one using your own concept art, it doesn't *need* to be much more than a thumbnail that tells you what it is. If it's going to a modeler for 3D, it probably needs to show three dimensionality and form from multiple angles. If it's going to a texture artist, it probably needs a sense of materials. If it's going to a rigger/animator, it needs some examples of how it will be posed and what the limits of those poses are. If it has to talk or emote, then expressions will be necessary to show. Very, very few character designs can accomplish everything they need in one image.
For my Egil's Saga project, I'm going to be using my sketches to design my world. I can get away with a very rough level of finish, although if the goal is to show my ability for an employer, it makes sense to take it further than that.
You'll note that I didn't talk about story. Unlike illustrations, designs don't really need to tell stories by themselves. You need to express how they can be used to do that, but most designs don't need a visual context to work as a design. Often however, they need that visual context to *prove* that they work as a design, so a final illustration is quite common. Due to concept art books, that illustration frequently gets labeled as "concept art", but it is not really part of the design process - It's just proof that the design does what it needs to, and answers the questions that will come up.
Obviously, this is my point of view, and different studios and different projects may think of the process differently. I'd love to hear if you think I've mis-represented things, or if you design in another way. Thanks for reading!