A valley is a low area of land between hills or mountains, usually with a river or stream running through it. Picture two mountain ranges rising up on either side, and the long, lower stretch of land between them is the valley. Rivers often flow through valleys because water naturally runs downhill, carving the land deeper over thousands of years.

Valleys have been important to human civilization throughout history. The rich soil carried down from the mountains often makes valley floors excellent for farming. Many major cities grew up in valleys because the flat land was perfect for building, the rivers provided water and transportation, and the surrounding mountains offered protection. California's Central Valley, for instance, produces much of America's fruit and vegetables.

The word can also describe a low point in other situations. If your basketball team wins ten games, then loses five in a row, then starts winning again, those losses represent a valley in your season. In this sense, valleys are the opposite of peaks or highs.

Geographers distinguish between different types of valleys based on how they formed: U-shaped valleys were carved by glaciers, while V-shaped valleys were cut by rivers over time.