In common terminology, a baby is the very young offspring of adult human beings, while infant (from Latin īnfāns 'baby, child') is a formal or specialised synonym. The terms may also be used to refer to juveniles of other organisms. A newborn is, in colloquial use, a baby who is only hours, days, or weeks old; while in medical contexts, a newborn or neonate (from Latin neonātus 'newborn') is an infant in the first 28 days after birth (the term applies to premature, full term, and postmature infants).
Infants born prior to 37 weeks of gestation are called "premature", those born between 39 and 40 weeks are "full term", those born through 41 weeks are "late term", and anything beyond 42 weeks is considered "post term".
