A newborn is a baby that has just been born, typically defined as being from birth to about two months old. During this stage, newborns undergo rapid physical and developmental changes. They usually weigh between 5.5 to 10 pounds and measure about 18 to 22 inches in length. Their senses are developing, but they primarily respond to touch, sound, and light. Newborns require constant care, including feeding, diaper changes, and sleep. They typically sleep 16 to 18 hours a day, waking every few hours to eat. Parents often seek guidance from healthcare professionals, such as pediatricians, to ensure their newborn's health and well-being.