红叶是指落叶植物在秋天的几周之间，叶子由绿转红的现象。在温带地区，如东北亚及北美洲，红叶是吸引观光客的重要旅游资源。

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of red, yellow, purple, black, orange, pink, magenta, blue and brown. The phenomenon is commonly called autumn colours or autumn foliage in British English and fall colors, fall foliage, or simply foliage in American English.