Deciduous means "falling off at maturity" or "tending to fall off". Deciduous plants lose their leaves for part of the year. In colder lands, leaf loss coincides with winter. In warmer lands, such as tropical, subtropical and arid lands, deciduous plants may lose their leaves during dry seasons or during times when there are changes in rainfall.
Coniferous woodland, coniferous plants keep their leaves year round. Most plants in tropical rain forests keep their leaves all year, gradually replacing them as they fall with age. Fewer plants are green year-round in cooler climates, but conifers are dominant when the climate becomes too cold for broad-leafed plants.
Whereas deciduous plants lose their leaves as an adaptation to cold or dry seasons, coniferous plants keep their leaves year round as an adaptation to low nutrient levels (so that they don't have to expend nutrients in the creation of new leaves).