A kingdom is a country ruled by a king or queen. The monarch (the ruler) usually inherits their position, meaning they become king or queen because their parent was the monarch before them. Throughout history, kingdoms have been one of the most common forms of government. Ancient Egypt was a kingdom ruled by pharaohs. Medieval Europe was divided into many kingdoms, like France, England, and Spain.

Today, some kingdoms still exist, though most modern monarchs share power with elected governments. The United Kingdom, for instance, has a king or queen, but elected officials make most of the important decisions.

In biology, kingdom means something completely different: one of the largest groups scientists use to classify living things. Every organism belongs to a kingdom based on its basic characteristics. The animal kingdom includes everything from elephants to ants. The plant kingdom includes trees, flowers, and grass. Other kingdoms include fungi (like mushrooms) and various types of microscopic organisms. When a biologist discovers a new species, one of the first questions is: which kingdom does it belong to?

The word can also describe any realm or domain where someone or something rules. A lion might be called the king of the jungle, ruling over his kingdom of the savanna.