A gobo is an object placed inside or in front of a light source to control the shape of the emitted light and its shadow.[1][2][3][4][5]
For studio photography purposes, the term "gobo" has come to refer to any device that casts a shadow, and various pieces of equipment that go in front of a light (such as a gobo arm or gobo head).[6]
In theatrical lighting, however, the term more specifically refers to a device placed in "the gate" or at the "point of focus" between the light source, called a lamp, and the lenses (or other optics).