Active Cathedral denotes a currently active cathedral, co-cathedral, pro-cathedral, or proto-cathedral.
A cathedral is the personal church of the hierarch who rules a canonical jurisdiction and contains his throne or cathedra.
Co--cathedrals exist when there are two (or, rarely, more) active cathedrals in a canonical jurisdiction. Technically, each is so termed and each is of equal precedential rank. In common usage, however, the term is often only used of the second church so designated, unless both are either of equal antiquity or each was a cathedral in its own right prior to the two being designated as co-cathedrals.
The most common circumstances that might cause there to be co-cathedrals include:
The dignity of co-cathedral has also been conferred on a church: as a sign of particular honor due to its antiquity, historical importance, or spiritual significance; in recognition of an event that transpired there; in gratitude for a service performed by its clergy or faithful; or, as a mark of hierarchical affection. Such is both uncommon and inconsistent with the intended usage of the dignity, but does occur.
A pro-cathedral is a church temporarily designated to serve as or in lieu of a cathedral.
Such a designation may be made:
A proto-cathedral is a church that formerly had the dignity of a cathedral. Properly, the term is applied to that church which was the first (proto) cathedral in a canonical jurisdiction. Occasionally, the styling 'Old Cathedral' is incorporated into the church name as an alternative (an example of such is St Patrick's Old Cathedral - NYC).
There are, additionally, such designations as metropolitan cathedral and patriarchal cathedral, applied to the cathedrals which are the seats of those respective hierarchs.