reredos

A reredos is an ornamental screen or partition, typically made of wood or stone, that is placed behind an altar in a church. It is not directly attached to the altar table but is affixed to the wall behind it. The term "altar screen" is also used to describe this structure.123

Reredoses are a form of altarpiece, which are works of art decorating the space above and behind the altar. These artworks can include paintings, reliefs, or sculptures and usually depict religious subjects. The practice of erecting structures behind altars dates back to at least the 11th century, with sculpture being a dominant element in the Middle Ages and paintings becoming more common later.2