A Trellis is a structure, usually made from interwoven pieces of wood, bamboo or metal that is often made to support a climbing plant or plants. There are many types of trellis for different places and for different plants, such as sweet peas, grapevines, ivy or other support based growing plants.
A trellis can also refer to a structure, usually made from interwoven wood pieces, attached to the roof or exterior walls of a house. A pergola is a typical example of a garden feature forming a shaded walk or passageway of pillars that support cross beams and a sturdy open lattice, upon which woody vines are trained.
While metal trellises are typically very ornate, they may not be the best choice for many vinning plants. As the sun beats on the metal, it gets very hot, and actually stunts the growth of many vines. For tender plants such as sweet peas, beans, and morning glories, wood or string are the preferred choices.