Newborn and neonate.  In general context, a newborn is an infant who is within hours, days, or up to a few weeks from birth.

In medical context, newborn or neonate (from Latin, neonatus, newborn) refers to an infant in the first 28 days of life (less than a month old).

[2] The term "newborn" includes premature infants, postmature infants and full term newborns.