Other terms can be used to describe the baby's stage of development. These terms do not follow clear rules and are used differently by different people, and in different regions. For example, "infant" may be used until the baby can walk, while some use "infant" until the baby is one year old. From birth until 3 months of age, a baby can be called a "newborn". Depending on how many weeks gestation at birth, newborns may be called premature, post-mature, or full term. The word "infant" comes from Latin: "infans" means "unable to speak". 