Mast is the fruit of forest trees and shrubs, such as acorns and other nuts. The term derives from the Old English mæst, meaning the nuts of forest trees that have accumulated on the ground, especially those used historically for fattening domestic pigs, and as food resources for wildlife. In the aseasonal tropics of Southeast Asia, entire forests, including hundreds of species of trees and shrubs, are known to mast at irregular periods of 2–12 years.