What type of trait appears only when an organism inherits two of them?

A recessive trait is a characteristic that manifests in an organism only when it has inherited two copies of the recessive allele, one from each parent. This means that both alleles must be of the recessive type for the trait to be expressed.

In contrast, a dominant trait requires only one copy of the dominant allele to be expressed, so it can appear even if the organism has just one dominant allele paired with a recessive one. Codominant traits involve both alleles being expressed equally in the phenotype, which differs from the scenario presented in the question. The term "inherited trait" is a broader term that encompasses both dominant and recessive traits, but does not specify the requirement for expression.

Thus, the specific nature of how recessive traits work makes them uniquely characterized by their expression only in the presence of two recessive alleles, which is why this choice is accurate.