What term describes specific characteristics that define an individual?

The term that describes specific characteristics defining an individual is "trait." In genetics and biology, traits are specific features or attributes of an organism, which can range from physical characteristics, such as eye color or height, to behavioral qualities. Each trait is influenced by genetic makeup and, in some cases, environmental factors.

While "genotype" refers to the specific genetic constitution of an individual, it may not directly represent observable characteristics. "Phenotype" encompasses the observable physical and biological traits of an organism that result from the interaction of its genotype with the environment, but again, it is broader than simply defining unique characteristics. "Attribute" is a more general term that can refer to features of anything and is not specifically tied to biological context like traits are. Thus, "trait" is the most precise term among the options given for describing the specific characteristics that distinguish an individual.