A "defining trait" refers to a characteristic or quality that is unique or essential to a person, object, or concept, making it easily identifiable or giving it its distinct identity. Full definition
Good players that have one defining trait in their play. (justarsenal.com)
The only defining trait is its screwed - up sense of feminism. (freshfiction.tv)
Each is assigned their own defining traits for the purpose of the film, leaving its actors to breathe full life into them, which they do effortlessly. (scene-stealers.com)