greenbelt

/ˈɡrinˌbɛlt/
noun
  1. An area of open land, often with trees and grass, around a city where building is limited to protect nature and provide recreation.
    • We went for a bike ride along the greenbelt that surrounds the town.
    • The city council voted to expand the greenbelt to preserve more farmland.
    • Houses are not allowed to be built in the greenbelt to keep the area natural.