A crown princess is a daughter of a monarch, who also happens to be the heir to the throne. In some monarchies the firstborn child is the heir regardless of gender, and a firstborn girl will therefore always be crown princess (this is known as cognatic succession).

In other monarchies sons will have a right to the throne before daughters, and a younger son could therefore be crown prince instead; degrading the former crown princess to princess (known as agnatic-cognatic succession). Finally, a certain few monarchies will have a fully agnatic succession which mean that they do not allow females to be monarchs (or, of course, crown princesses) at all.