A baby can have several possible meanings in the
field of medicine, including: a) a newborn child, b) a
child under the age of one year (some definitions go
out to three years of age), c) an extremely young
child or animal, especially one that is not yet able to
walk or talk (in the case of humans), d) the young of
any mammal or animal, or e) to treat gently or with
special care. When applied to humans, the term
“baby” means the same thing as infant.

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There are different terms used depending on the age of the baby. Specifically, a newborn
(also known as a neonate) is a baby that is hours, days, or weeks old (up to 28 days). A
full-term baby or infant is one that was born around the time of the due date (around 40
weeks gestation).

A premature baby or infant is one that is born less than 37 weeks gestation. A
postmature baby is one that is born after 43 weeks gestation. Prior to birth, the term
fetus is used to described the developing being.

Baby comes from the Middle English word "babe," which is an imitation of sounds that
babies make.
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