A dike (also spelled dyke) is a wall or embankment built to hold back water and prevent flooding. The Netherlands is famous for its dikes, which protect large areas of low-lying land from the sea. Without dikes, much of the country would be underwater during storms or high tides.

Dikes are usually made of earth, stone, or concrete, and they need to be strong enough to withstand tremendous water pressure. Building and maintaining dikes requires careful engineering: a weak spot or break in a dike can cause catastrophic flooding. The Dutch have been building dikes for over a thousand years, creating a system so effective that it has inspired similar projects around the world.

There's a famous story about a Dutch boy who saved his town by plugging a leak in a dike with his finger until adults could repair it. While this tale is fiction, it captures an important truth: dikes require constant attention and maintenance to keep communities safe.

The word can also refer to a long wall of rock formed by volcanic activity underground, though this geological meaning is less common in everyday conversation.

Note: The spelling dyke is also used as a slur for a lesbian. In this definition, it refers only to the water barrier.