A bird's wing is based on an aerodynamic shape called an airfoil. It is curved outward along the entire upper surface, to produce an upward force known as lift [1].
Reference[]
^France, Peter; et al. (2007). Bird: The Definitive Visual Guide. Dorling Kindersley Inc. ISBN9780756631536. CS1 maint: Explicit use of et al. (link)
This article is part of Project Glossary, an All Birds project that aims to write comprehensive articles on each term related to animals.