What does this equation mean?

Sewall Wright’s 1931 paper, “Evolution in Mendelian Populations,” added the piece Fisher’s and Haldane’s more deterministic treatments lacked: a formal account of genetic drift, the random change in allele frequency from generation to generation caused by finite population size [ 3 ] . Wright showed that in a randomly mating population of effective size $N_e$ , the variance in allele frequency change per generation from sampling alone is $\operatorname{Var}(\Delta p) = \frac{p(1-p)}{2N_e}$. for a diploid population starting at allele frequency p . This single expression carries a real consequence: small populations can fix or lose alleles by chance alone, independent of whether those alleles are beneficial, neutral, or mildly deleterious, and the smaller the effective population, the faster that random fixation proceeds. Wright’s “shifting balance” framework, in which small subpopulations explore a rugged fitness landscape partly by drift and partly by selection, remains debated in its strong form, but the underlying mathematics of drift is uncontroversial and became a permanent part of population genetics.