Final answer:
The equilibrium between natural selection removing deleterious alleles and mutations introducing them is known as mutation-selection balance.
Step-by-step explanation:
The point at which the rate at which a deleterious allele is being eliminated from a population by natural selection is in equilibrium with the rate at which this allele is replaced by a new mutation is called the mutation-selection balance. This concept falls under population genetics, where it is acknowledged that mutations are the ultimate source of genetic variation.
Deleterious alleles can be swiftly eliminated from the gene pool unless they are continuously introduced through new mutations. Beneficial mutations, however, may spread through the population, a process that can also be affected by genetic drift. Over time, the interplay between these factors contributes to the adaptive evolution of a population, shaping its genetic structure and diversity.