A forest is a large area densely covered with trees and undergrowth. When you walk into a forest, you might notice how the tree canopy blocks much of the sunlight, creating cool shade below. The air smells different: rich with decaying leaves and damp soil. Birds call from branches overhead, while smaller creatures rustle through the underbrush.

Forests come in many varieties. Tropical rainforests near the equator stay warm and wet year-round, supporting incredible biodiversity: colorful birds, monkeys, insects, and plants found nowhere else. Temperate forests, common in places like the eastern United States, experience four distinct seasons, with trees that lose their leaves each fall. Coniferous forests in northern regions stay green all year, filled with pine, spruce, and fir.

Forests do crucial work for our planet. Trees absorb carbon dioxide and release oxygen, purify water as it filters through soil, and prevent erosion by holding dirt in place with their roots. They provide homes for countless species and materials humans have used for millennia: wood for building, fuel for fires, and food like nuts and berries.

The word can also describe any dense collection of tall things: a forest of skyscrapers downtown, or a forest of hands shooting up when the teacher asks who wants to answer.