A building made of glass or transparent material, with or without a floor where plants are grown is a greenhouse. Can be portable or permanent, the main purpose is to extend the growing season of flowers, vegetables, fruits, and transplants.
Certain crops can be grown in a greenhouse year round. A greenhouse allows the gardener to control the main factors that affect plant growth--- light, moisture, and temperature. the house also allows the gardener to control and combat pest and diseases.
There are different kinds of greenhouses you have shelves with plastic or polyethylene covering it that are portable. These are small so you can move them in and out depending on the weather. There are Cold frame style houses that cover your plants in the ground to help protect from frost and drying winds.
poly-tunnel is a tunnel made of polyethylene in a semi-circle shape. The interior heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure.