A priest acquaintance, Fr. Bede Rowe, has on his interesting blog A Chaplain Abroad, an entry about a veil for a ciborium.
A ciborium is a sacred vessel which resembles a chalice but with a cover used for hosts to be consecrated and consecrated Hosts to be reserved in the tabernacle for distribution.
Since a ciborium is a sacred vessel, it ought to be consecrated, like the hands of the priest who carry them.
Ciborium is also an feature of a sanctuary of a church, the canopy on columns over an altar. It is also called a baldachin.
The sign that the Eucharist is present is first and foremost the veil. The baldachin is the veil over the altar. There should be a veil over the tabernacle when the Eucharist is present. When the Eucharist is carried away from the altar, expect for distribution to the faithful, a canopy or ombrellino is used.
Think of it this way. In the Old Testament, when God descended on the mountain or the tent to speak with Moses, the place was engulfed by a cloud into which Moses had to enter. This was a manifestation of God’s divine attribute of glory. The veil on sacred vessels hearkens to this glorious cloud.
The ciborium, even in the tabernacle, ought to have a veil over it. I have noted that in many parish tabernacles, ciboria don’t have veils.