The principal says that allete frequencies in a population are stable and constant from generation to generation. The gene pool (total genes and their alleles in a population) remains constant, this is called genetic equilibrium. The sum of all the all the frequencies is 1. For exmple- In a diploid p and q denote the frequency of A and a. The frequency of AA is `p^(2)` and aais `q^(2)` and of Aa is 2pq. This `p^(2)+q^(2)2pq=1` which means `(p+q)^(2)=1`. When frequency measured differs from expected frequencies the difference in frequencies indicates the extent of evolutionary change. The equilibrium is distributed by 1-gene migration 2-mutation 3- genetic drift 4- natural selection.
Distribution in genetic equilibrium, or Hardy-Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.
