Sub-replacement fertility

Sub-replacement fertility is a total fertility rate (TFR) that (if sustained) leads to each new generation being less populous than the older, previous one in a given area. The United Nations Population Division defines sub-replacement fertility as any rate below approximately 2.2 children born per woman of childbearing age, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates.

Source: Wikipedia — Sub-replacement fertility (CC BY-SA 4.0)