The probability of a child born in a specific year or period dying before reaching the age of 5 years, if subject to agespecific mortality rates of that period, expressed per 1000 live births.
The under-five mortality rate as defined here is, strictly speaking, not a rate (i.e. the number of deaths divided by the number of population at risk during a certain period of time) but a probability of death derived from a life table and expressed as a rate per 1000 live births.
