Wiktionary
n. A small piece of detailing added to break up the surface of an object and add visual interest, particularly in movie special effects.
Wikipedia
thumb|upright=1.5|A cube and a greebled version A greeble or nurnie is a fine detailing added to the surface of a larger object that makes it appear more complex, and therefore more visually interesting. It usually gives the audience an impression of increased scale. The detail can be made from simple geometric primitives (such as cylinders, cubes, and rectangles), or more complex shapes, such as pieces of machinery (cables, tanks, sprockets). Greebles are often present on models or drawings of fictional spacecraft or architectural constructs in science fiction and are used in the movie industry ( special effects).