What does it mean if my daughter is in the 10th percentile for head circumference?

Population norms. Growth features including head circumferancee, length and weight have been collected over the years and publishes as basic guidelines for following growth in kids.The average of all would be at 50% while some would be on the larger or smaller size. The 10% means only that of 100 kids born on the same day, her head is larger than 10% but smaller than 90%.