A greenhouse is a structure which allows people to regulate climatic conditions, such as temperature and humidity. There are many different designs of greenhouses, however in general these buildings include large areas of transparent material to capture the light and heat of the sun. The three most common transparent materials used in the roof and walls of modern greenhouses are rigid plastics made of polycarbonate, plastic films made of polyethylene or glass panes. When the interior of a greenhouse is exposed to sunlight, the internal temperature rises and shelters the plants from cold weather.

The word greenhouse can be used interchangeably with the terms glasshouse and hothouse, depending on the building's material and heating system. Buildings today are more commonly referred to as greenhouses because they can be constructed of a variety of materials, like wood and polyethylene plastic. A glasshouse on the other hand is a more traditional style of greenhouse that is only constructed with panes of glass to allow light into the building. The term hothouse implies that the greenhouse is heated through artificial means, however both heated and unheated structures can be defined generally as greenhouses.

Greenhouses can range in size from small sheds to industrial-sized buildings and enormous glasshouses. The smallest example is a miniature greenhouse known as a cold frame, typically used at home. Whereas large commercial greenhouses are high tech production facilities for vegetables, flowers or fruits. The glass greenhouses are filled with equipment including screening installations, heating, cooling, and lighting, and may be controlled by a computer to optimize conditions for plant growth. Different techniques are then used to manage growing conditions, including air temperature, relative humidity and vapour-pressure deficit, in order to provide the optimum environment for cultivation of a specific crop.