An infant is a formal or specialised synonym for the common term baby, meaning the very young offspring of human beings. The term may also be used to refer to juveniles of other organisms. A newborn is, in colloquial use, an infant who is only hours, days, or up to one month old. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth; the term applies to premature, full term, and postmature infants. Before birth, the term fetus is used. The term infant is typically applied to very young children under one year of age; however, definitions may vary and may include children up to two years of age. When a human child learns to walk, the term toddler may be used instead.