A princess is the daughter of a king or queen, or the wife of a prince. Some children like to have princess parties because they get to wear fancy dresses, tiaras, and little plastic high heels.
In countries that are monarchies, rulers are born into their positions and are typically called kings and queens. If they have a daughter, she’s a princess. Women who marry into these families can also become princesses. The popular image of a princess might be Cinderella dressed for the ball, but modern princesses look a lot more like ordinary people. Princess is the feminine form of prince, from the Latin princeps, "chief leader."