It is generally believed that the development of breasts before the age of eight in girls, and the onset of menstruation before the age of ten; in boys, the development of testicles before the age of nine, appearance of secondary sexual characteristics, and accompanied by rapid physical development, are referred to as precocious puberty. Early development refers to the situation where, before puberty, not only the sexual organs but also other organs in boys and girls begin to develop simultaneously.

Therefore, precocious puberty and early development not only differ in the age of onset but also focus more on whether the sexual organs are developing in coordination with the body's other organs. The differences lie not only in the timing but primarily in whether the development of the sexual organs is coordinated with the development of the body's other organs. If the sexual organs and the body's other organs are not developing in coordination, it indicates precocious puberty. If they are coordinated, and merely occurring earlier than usual in puberty, it is considered early development.