A work or ensemble placed on, above, or behind an altar, frequently combining sculpture, painting, architecture, gilding, and narrative imagery.
An altarpiece is an artistic work or ensemble associated with an altar. It may be painted, carved, architectural, or mixed-media, and may take the form of a single panel, triptych, polyptych, retable, or monumental sculptural construction.
Etymology
English compound altar + piece.
Sculptor Notes
The altarpiece is an ideal example of sculpture working with architecture rather than as an isolated object. Scale, framing, central axis, predella, niches, saints, narrative relief, gilding, and the architecture of the church should be conceived as one visual order.
References
https://www.metmuseum.org/art/collection/search/475525; https://www.metmuseum.org/art/collection/search/463377