A kingdom is a territory or group of people ruled by the same monarch. You probably know the story of the prince who searched the kingdom to find the girl who left her glass slipper at the ball.
A kingdom is a place — either literal or imagined — where someone or something reigns. A queen rules over her kingdom, which is land and the people who live on it, while a certain pop singer has a kingdom of young fans. In "the kingdom of the mind," creativity and imagination — not kings or queens — rule. In biology, a kingdom is a grouping of like organisms. For example, a dog is a member of the animal kingdom.