A gobo is an accessory that, when fit into the appropriate lamp, causes an image to be projected on the cyc, floor, or wherever it might be pointed. It is a piece of metal with a design cut in it. The light shines through it, showing the cut-out areas.

The gobo is held in place by a gobo paddle, which is then inserted into a slot in either a profile spot or possibly (though not usually) a follow spot. Gobos can either be ordered or made out of metal designed for high temperatures, such as that used in an aluminum baking pan.

In Stagecraft, students tried their hand at creating a gobo. Some turned out quite well. Mine were hopeless, so I doubt I'll be turning gobo-making into a career.

My Gobos A Projected Gobo Making Gobos in Class