Definitions for "Life expectancy at birth"
The number of years newborn children would live subject to the mortality risks prevailing for the cross-section of population at the time of their birth.
The number of years a newborn infant would live if prevailing patterns of mortality at the time of its birth were to stay the same throughout its life. First use 1877 (OED).
The number of years a newborn infant would live if prevailing patterns of mortality at the time of birth were to stay the same throughout the child's life.