what term describes a type of trait that is usually expressed only when an organism has two identical alleles for that trait

Recessive allele is the term that describes a type of trait that is usually expressed only when an organism has two identical alleles for that trait.

Recessive alleles are various genetic codes that do not produce a phenotype when a dominant allele is present. Recessive allele is only expressed if the individual has two copies of the allele (known as homozygous). For example, the allele for brown hair is recessive, thus, for an individual to have brown hair, he must possess two copies of the 'brown hair' allele.