An architectural canopy supported on columns over an altar; not to be confused with the lidded Eucharistic vessel also called a ciborium.
In architectural usage, a ciborium is a canopy supported on columns over an altar. Medieval examples often use marble, mosaic, inlay, and carved capitals. The term must be distinguished from the lidded Eucharistic vessel that is also called a ciborium.
Etymology
From Greek kiborion and Latin ciborium; the word later acquired several ecclesiastical meanings.
Sculptor Notes
Architectural ciboria create a small building around the altar. Their columns and canopy frame rather than block the sacred focus. A sculptor working on one must coordinate ornament with long-distance legibility and the vertical thrust of the surrounding church.
References
https://www.metmuseum.org/art/collection/search/463315