An infant (from the Latin word infants, meaning “unable to speak” or “speechless”) is the more formal or specialized synonym for “baby”, the very young offspring of a human or other animal.
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 post-mature infants; before birth, the term “fetus” is used. The term “infant” is typically applied to young children between one month and 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.
In British English, “infant” is a term that can be applied to school children aged between four and seven. As a legal term, “infancy” continues from birth until age 18.
Infants respond to the sound of snake hissing, angry voices of adults, the crackling sound of a fire, thunder, and the cries of other infants. They have a drop in heart rate, their eyes blinking, increased turning toward the speakers or parent, all of these indicating that they were paying more attention. This is believed by some to be evolutionary response to danger.