Deciduous means "temporary" or "tending to fall off" (deriving from the Latin word decidere, to fall off).

Deciduous plants, principally trees and shrubs, are those that lose their foliage for part of the year. In most cases, the foliage loss coincides with the incidence of winter in temperate or polar climates, but some plants lose their leaves during dry seasons in arid climates . Non-deciduous plants are known as evergreens.

Deciduous teeth, also called milk teeth, are those that fall out during the course of normal development. Other body parts that are shed, such as antlers, are also described as deciduous.