Which term describes the observed trait of an organism that masks the recessive form of a trait?

The term that describes the observed trait of an organism which masks the recessive form of a trait is "dominant." In genetics, when two alleles for a trait are present, the dominant allele is the one that is expressed in the phenotype, meaning it will determine how that trait appears in the organism. For example, if one allele is dominant and another is recessive, the dominant allele will be the one that is visibly represented, while the effect of the recessive allele will not be observed in the phenotype.

In contrast, the term "recessive" refers to the allele that does not produce a visible effect when a dominant allele is present. "Heterozygous" describes an organism that has two different alleles for a specific gene, including one dominant and one recessive allele, but does not describe the traits themselves. The term "phenotype" refers to the observable characteristics or traits of an organism, which result from the interaction of its genotype and the environment, but this term does not specifically indicate the masking capability of a trait. Therefore, "dominant" is the most accurate term to identify the trait that masks the effect of a recessive trait.