What does idiosyncrasy refer to in a person's behavior?

Idiosyncrasy refers to a characteristic or behavior that is peculiar to an individual, making it unique or distinctive to them. It often highlights a quirky trait, mannerism, or preference that sets a person apart from the norm. This term conveys the idea of individuality and particularity, emphasizing the unique aspects of someone's behavior that may not be easily relatable to others.

In contrast, the other choices refer to broader or more commonly shared traits or beliefs. For instance, a common trait suggests something widely shared among many people, while a universal belief indicates an idea that is accepted by all. Traditional norms refer to established practices or standards upheld within a group, which do not encompass the unique, personal nature that idiosyncrasies imply.