A cyclorama is a large curtain or wall, often concave, positioned at the back of the apse. It was popularized in the German theater of the 19th century and continues in common usage today in theaters throughout the world. A "cyc" (US theatrical abbreviation) can be made of unbleached canvas (larger versions) or muslin (smaller versions), filled scrim (popularized on Broadway in the 20th century), or seamless translucent plastic (often referred to as "Opera Plastic"). Traditionally it is hung at 0% fullness (flat). When possible, it is stretched on the sides and weighted on the bottom to create a flat and even surface. As seams tend to interrupt the smooth surface of the cyclorama, it is usually constructed from extra-wide material.
As the name implies, it often encircles or partially encloses the stage to form a background.
An infinity cyclorama (found particularly in television and in film stills studios) is a cyc which curves smoothly at the bottom to meet the studio floor, so that with careful lighting and the corner-less joint, the illusion that the studio floor continues to infinity can be achieved. Cycloramas or "cycs" also refer to photography curving backdrops which are white to create no background, or green screen to create a masking backdrop.
Cycloramas are often used to create the illusion of a sky onstage. By varying the equipment, intensity, color and patterns used, a lighting designer can achieve many varied looks. A cyclorama can be front lit or, if it is constructed of translucent and seamless material, backlit directly or indirectly with the addition of a white "bounce" drop. To achieve the illusion of extra depth, often desirable if one is re-creating a sky, the cyclorama can be paired with a "sharkstooth scrim" backdrop. A dark or black scrim, by absorbing the extraneous light which is commonly reflected off the floor of the stage from the acting areas, can help the lighting designer achieve deeper colors on the cyclorama. Cycloramas are also often illuminated during dance concerts to match the mood of a song.
Occasionally, the cyc may be painted with a decorative or pictorial scene to fit a specific show; these are generally referred to as backdrops.