Roll moulding refers not to the decorative motif appearing on the moulding strip – rather to its general shape. The roll moulding shape is semi-circular bulging towards the viewer. If the moulding is concave, it is known as cavetto. If it is convex it is known as ovolo. If partly convex and partly concave it is known as cyma.
Local examples (click to enlarge)
St George's tower, main street (St George's Street)
St Stephen's church, Hales Drive, Hackington