The Apgar score is a system used to evaluate newborns on five criteria: heart rate, breathing effort, muscle tone, reflexes, and skin color. Scores are given on each criterion on a scale of 0-2 at one and five minutes after birth. The total score out of 10 indicates the baby's overall health, with lower scores potentially signifying need for extra care. Developed in 1952 by Dr. Virginia Apgar, it provides doctors a quick way to assess a newborn's condition at birth.