百叶（英语：Louver）是一种将多个细长的板子，取出一定间隔，平行对齐排列出的结构物，如百叶窗，由一片一片的窗片组成百叶。

百叶箱、百叶窗、百叶帘、百也门，皆是用上百叶的常见物。

A louver (American English) or louvre (British English) is a window blind or shutter with horizontal slats that are angled to admit light and air, but to keep out rain, direct sunshine, and noise. The angle of the slats may be adjustable, usually in blinds and windows, or fixed.