A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations Food and Agriculture Organization (FAO) defines a forest as, Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban use. Using this definition, Global Forest Resources Assessment 2020 (FRA 2020) found that forests covered 4.06 billion hectares (10.0 billion acres; 40.6 million square kilometers; 15.7 million square miles), or approximately 31 percent of the world's land area in 2020.

Forests are the predominant terrestrial ecosystem of Earth, and are found around the globe. More than half of the world's forests are found in only five countries (Brazil, Canada, China, Russia, and the United States). The largest share of forests (45 percent) are in the tropical latitudes, followed by those in the boreal, temperate, and subtropic domains.