What is characterization of a person? Is it who they are as a person like strong, lonely, and things like that?
Those are certainly part of it.
Characterization is a character's defining traits. It's what he is like to be around, what he will or won't do under duress,, how far he will go to defend his beliefs, and how seriously he takes his relationships.
The best characters come up short, and have weaknesses the reader or viewer can relate to. Don Draper is riveting in a way that Joe Friday is not.