An iwan is a rectangular hall or space, usually vaulted, walled on three sides, with one end entirely open. The formal gateway to the iwan is called pishtaq, a Persian term for a portal projecting from the facade of a building, usually decorated with calligraphy bands, glazed tilework, and geometric designs. Since the definition allows for some interpretation, the overall forms and characteristics can vary greatly in terms of scale, material, or decoration.