Baby/ˈbeɪbi/ Definition 1 of 5Pro Tip 1/3Age Specific The term 'baby' usually refers to humans under 2 years old. Her baby just learned to walk. Pro Tip 2/3Not Only Newborns 'Baby' can mean a child still much reliant on parents, not just newborns. She’s holding her baby in the park. Pro Tip 3/3Gender Neutral The word 'baby' is gender-neutral; add 'boy' or 'girl' for specifics. They're expecting a baby girl in July.