The condition in which a gene in a homozygous recessive condition (aa) masks the effect of one or both members (BB or bb) of another gene pair is known as

The condition in which a gene in a homozygous recessive condition (aa) masks the effect of one or both members (BB or bb) of another gene pair is known as Recessive epistasis.
Recessive epistasis is when the recessive allele of one gene hides the expression of all alleles of another gene. As the masking allele is in this case recessive, this is called recessive epistasis.