Zero population growth

Zero population growth, sometimes abbreviated ZPG (also called the replacement level of fertility), is a condition of demographic balance where the number of people in a specified population neither grows nor declines, considered as a social aim by some. According to some, zero population growth is the ideal towards which countries and the whole world should aspire in the interests of accomplishing long-term environmental sustainability. What it means by ‘the number of people neither grows nor declines’ is that births plus in-migrants equal deaths plus out-migrants.