Which term describes an observable characteristic of an organism?

The term that describes an observable characteristic of an organism is "phenotype." The phenotype encompasses all the physical and observable traits of an organism, which may include attributes such as height, eye color, flower color in plants, and other traits that can be seen or measured. This concept is distinct from genotype, which refers to the genetic makeup of an organism, including both the dominant and recessive alleles present. While alleles are specific versions of a gene that can determine traits, and chromatids refer to the duplicated chromosomes during cell division, they do not directly describe observable characteristics. Therefore, phenotype is the correct term in this context, as it specifically focuses on outward features that are expressed as a result of the interaction between genotype and the environment.