APPSC Miscellaneous-2023 While "child mortality" can sometimes refer broadly to deaths of children, in standard demographic and public health contexts (like those used by UNICEF and WHO), it most often implies "under-five mortality", which is the probability of a child born in a specific year or period dying before reaching the age of five. Infant mortality specifically refers to death before the 1st birthday. Given the options, the 5th birthday is the most appropriate interpretation for general "child mortality".