Definitions for "Effective population size"
The equivalent number of breeding adults in a population after adjusting for complicating factors, such as non-random variation in family size or stochastic fluctuation in population size.
The size of an idealized population that shows the same amount of genetic drift as the population studied. This is approximately 10,000 individuals for humans, in contrast to the census population size of 6 109.
The population size that is relevant for random genetic drift. The actual number of individuals in a population that are reproducing.