A pergola is a garden feature forming a shaded walkway, passageway, or sitting area of vertical posts or pillars that usually support cross-beams and a sturdy open lattice, often upon which woody vines are trained. The origin of the word is the Late Latin pergula, referring to a projecting eave. As a type of gazebo, it may also be an extension of a building or serve as protection for an open terrace or a link between pavilions. They are different from green tunnels. Pergolas are sometimes confused with arbours, and the terms are often used interchangeably. An arbour (or arbor in the USA) is generally regarded as a wooden bench seat with a roof, usually enclosed by lattice panels forming a framework for climbing plants. A pergola, on the other hand, is a much larger and more open structure and does not normally include integral seating.