An infant or baby is the very young offspring of human beings. Infant (from the Latin word infans, meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term baby. The terms 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, a newborn or neonate (from Latin, neonatus, newborn) is an infant in the first 28 days after birth; the term applies to premature, full term, and postmature infants. Before birth, the offspring is called a fetus. 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, they are called a toddler instead. Other uses In British English, an infant school is for children aged between four and seven. As a legal term, infancy is more like being a minor, and continues until a person reaches 18 years of age. Physical characteristics A newborn's shoulders and hips are wide, the abdomen protrudes slightly, and the arms and legs are relatively long with respect to the rest of their body. Head A newborn's head is very large in proportion to the body, and the cranium is enormous relative to his or her face. While the adult human skull is about one seventh of the total body length, the newborn's is about . Normal head circumference for a full-term infant is 33–36 cm at birth. At birth, many regions of the newborn's skull have not yet been converted to bone, leaving "soft spots" known as fontanels. The two largest are the diamond-shaped anterior fontanel, located at the top front portion of the head, and the smaller triangular-shaped posterior fontanel, which lies at the back of the head. Later in the child's life, these bones will fuse together in a natural process. A protein called noggin is responsible for the delay in an infant's skull fusion. During labour and birth, the infant's skull changes shape to fit through the birth canal, sometimes causing the child to be born with a misshapen or elongated head. It will usually return to normal on its own within a few days or weeks. Special exercises sometimes advised by physicians may assist the