In lighting for film, theatre and still photography, a cuculoris (occasionally also spelled cucoloris, kookaloris or cucalorus) is a device for casting shadows or silhouettes to produce patterned illumination. The word is sometimes shortened to cookie or coo-koo. The cookie is used to create a more natural look by breaking up the light from a man made source. It can be used to simulate movement by passing shadows or light coming through a leafy canopy.
Generally, cookies fall into three groups: hard cookies, made from thin plywood or heavy poster board with random shapes cut out of the body; soft cookies (often called "celo" cookies), made from plastic impregnated screen (the same screen one might find in a storm window), also with random shapes cut or burned out; and natural cookies, or brancholorises, which are simply tree limbs or other available things that can be placed between the light and the subject.
Many "old-school" grips would say that any unnatural pattern used to create a shadow is a cookie.
Cucolorises are sometimes thought of as a subset of the gobo category. A gobo is either a metal or a glass device, used inside a lighting instrument (or in very close proximity to a lighting instrument), used to create patterns, shadows, logos or silhouettes. Cucolorises differ in that they are used farther away from the lighting instrument and therefore, do not need to be as heat resistant. Gobos generally are used when a very crisp, well defined edge is needed for a silhouette or projected object.