Trait (biology) In biology, a trait or character is a feature of an organism. The term phenotype is sometimes used as a synonym for trait in common use, but strictly speaking, does not indicate the trait, but the state of that trait (e.g., the trait eye color has the phenotypes blue, brown and hazel). A trait may be any single feature or quantifiable measurement of an organism. However, the most useful traits for genetic analysis are present in different forms in different individuals. A visible trait is the final product of many molecular and biochemical processes.