A piece of metal with a pattern cut into it, placed between the lamp and the first lens in a theatrical lighting instrument. Gobos may be bought pre-cut, with images of clouds, trees, stars, windows, or vaguely random patterns (``break-up''). They can also be custom-cut. The result is the casting of a particular shadow on actors, set and stage.

The simplest ingredients for a gobo are an aluminium pie tin and an X-acto knife.