The wall was an upright structure used by architects and shipbuilders for defining an area and carrying a load. A wall could be for security, shelter, soundproofing, or, simply, for decoration. Walls were made from many different kinds of material. A unique wall was the transparency which was made of a transparent material, making it a kind of wall-window.
On Talos IV, the Talosians built their cells with transparencies. In 2254, when he was a captive, Captain Christopher Pike tested the strength of the transparency by throwing himself against it. (TOS: "The Cage")