Final answer:
Variable expressivity is the term that describes how different individuals with the same genotype can have a variation in phenotype, meaning that the trait can be expressed to different degrees or in different forms among these individuals.
Step-by-step explanation:
The term that refers to the fact that different people with the same genotype can have variation in phenotype is Variable expressivity. This concept means that individuals with the same genotype (genetic makeup) can show different degrees or types of the phenotypic expression, leading to a range in the severity or manner in which a trait is manifested.
While Codominance refers to a condition where both alleles for a gene are fully expressed in the heterozygous state, this is not the answer to the question as it does not directly relate to the variation in phenotype among individuals with the same genotype. Reduced penetrance is a situation where not all individuals with a given genotype express the expected phenotype, but again, this does not describe variation in severity or form of expression of the trait. Instead, Variable expressivity captures the idea that the phenotype can vary in intensity among individuals even when they share the same genotype.