A greenhouse is a structure whose walls and roof are mainly glass, plexiglass, plastic, or other transparent or translucent material. It is generally used for growing plants indoors, usually for commercial, agricultural, exhibition, or research purposes. These include facilities for museum-like conservatories, as well as small sheds for indoor gardening.

The general purpose of a greenhouse is to replicate an outdoor environment indoors, although the climate and conditions created inside may be very different from those of the surrounding outdoor area.

The transparent or translucent enclosure applies to both the walls and roof. Plant-growing sheds and larger exhibition conservatories can share this form even when their size and internal climate differ.