What term is used for the physical expression of a trait?

The term that refers to the physical expression of a trait is "phenotype." This concept encompasses the observable characteristics of an organism, which can include its morphology, development, biochemical properties, and behavior. The phenotype results from the interaction of the organism's genotype with the environment.

In contrast, the genotype refers to the genetic makeup of an organism, which determines potential traits but does not directly describe the observable characteristics. Characteristics and attributes are broader terms that may encompass various traits but do not specifically refer to the physical manifestation of those traits. Thus, the specificity of the term "phenotype" in this context makes it the correct choice, as it directly addresses the question about the physical expression of a trait.