The term oak can be used as part of the common name of any of several hundred species of trees and shrubs in the genus Quercus, and some related genera, notably Cyclobalanopsis and Lithocarpus.
The genus is native to the northern hemisphere, and includes deciduous and evergreen species extending from cold latitudes to tropical Asia and the Americas.
Oaks have spirally arranged leaves, with a lobed margin in many species; some have serrated leaves or entire leaves with a smooth margin.
The flowers are catkins, produced in spring.
The fruit is a nut called an acorn, borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6-18 months to mature, depending on species.
Oaks are hardwood trees, and the wood is commonly used in furniture and flooring.