Polders are low-lying areas of land that have been reclaimed from water, typically found in countries like the Netherlands. They are created by constructing dikes to hold back water from rivers, lakes, or seas, allowing the land to be drained and used for agriculture or habitation. The process of creating polders involves pumping out water and managing the water levels to prevent flooding. This land reclamation technique has been essential for Dutch agriculture and urban development, enabling the country to expand its usable land area despite being below sea level in many regions.