A more thorough explanation:

Definition: A daughter is a female child of a parent. It is a parent-child relationship where the child is a girl.

• My daughter is turning 10 years old next month.
• She is a proud mother of two daughters.
• The father was overjoyed when he found out he was having a daughter.

The first example shows a parent referring to their female child as their daughter. The second example shows a mother who has two female children, both of whom are her daughters. The third example shows a father who is happy to have a daughter, indicating that the child is a girl.