A polytunnel is a long, low building for growing plants. The bones are a row of hoops or a light frame. Over that frame people stretch plastic, so it becomes a kind of soft greenhouse: warmer inside, sheltered from wind and heavy rain. Farmers and gardeners use it for salad, tomatoes, flowers, seedlings. It is cheaper and quicker than a glass house, and you can take it down. This is mainly a British gardening and farm word. In American English people often say hoop house or high tunnel. Though actually, it is not a real tunnel you walk through under a hill; it only looks like a tunnel from the outside. The plastic is the same family of stuff as polythene sheeting, which is why the name is short for polythene tunnel. In Taiwan you have seen these on farms: the long plastic-covered houses in the fields.

隧道式塑膠溫室；塑膠隧道棚