Total Fertility Rate (TFR) is a demographic measure that estimates the average number of children a woman will have over her childbearing years, typically defined as ages 15 to 49. TFR is crucial for understanding population growth and decline, as it directly impacts a country's demographic structure, economic development, and migration patterns. A TFR of around 2.1 is often considered the replacement level, meaning it is the rate required to maintain a stable population without immigration.