Overhanging used as a mark of honor, named after Baghdad whence came the cloth originally used for this purpose. The more generic term for this covering is canopy. There are two chief forms of the fixed canopy: (1) the civory (ciborium ), a structure in stone, metal, or wood consisting of four or more columns, united by an arch or architrave, roofed, highly decorated, and built over an altar; (2) the baldachin (baldachino ) or tester, which is simpler in form and consists of a smaller, lighter structure of metal or wood (carved and gilded, and often adorned with textiles) either hung over an altar, or attached to the wall behind, like a bracket, or supported at the back by two pillars so that it juts over the altar like the canopy of a throne. A canopy of some form has been used as a mark of distinction over altars since the 4th century.
Another type of canopy is that placed over the throne of a "greater prelate," i.e., a cardinal anywhere, or a nuncio, apostolic delegate, archbishop, bishop, or abbot in the place of his jurisdiction, as a mark of honor and a sign of authority.
In the medieval period, a portable canopy—a collapsible, ornamental awning of silk or other precious material—sustained by four, six, or eight poles, or in the form of a large ornamental umbrella, was borne as a mark of honor over the Blessed Sacrament in procession, as well as over the pope, a cardinal legate at his solemn entry into the place of his legacy, and a bishop for his first solemn entry into his cathedral or other church of his diocese.
Bibliography: j. b. o'connell, Church Building and Furnishing (Notre Dame, IN 1955) 183–186. j. braun, I Paramenti sacri, tr. g. alliod (Turin 1914) 180–182, 215–217.
[j. b. o'connell/eds.]
"Baldachino." New Catholic Encyclopedia. . Encyclopedia.com. (September 25, 2018). http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/baldachino
"Baldachino." New Catholic Encyclopedia. . Retrieved September 25, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/baldachino