A cathedral is a church building presided over by a bishop, and therefore the central church building of a diocese, an administrative unit of the larger church. The cathedral is known in hierarchical Christian denominations such as the Catholic and Anglican Churches. A cathedral is often, though not always, a large, impressive building, and conversely, many large, imposing church buildings are not technically cathedrals.

The word cathedral is shortened from the term cathedral church, in which it is used as an adjective. A cathedral is a church containing the cathedra — Latin for "chair" — of the bishop. In the ancient world, the chair was a symbol of both a teacher and a magistrate, and therefore ideal for representing the power and duties of the bishop.

What makes a cathedral a cathedral is the presence of the bishop, not anything inherent in the building itself. Therefore, a church building may gain or lose cathedral status. Some cathedrals were built as cathedrals, but others were not. Church buildings that have lost cathedral status are called proto-cathedrals. In addition, a church building may serve temporarily as a cathedral, in which case it is termed a pro-cathedral.

In the Catholic Church, the cathedral system is more complex than a single cathedral church governing each diocese. Some dioceses have co-cathedrals that share authority. In addition to the simple cathedral church, there are cathedrals with increasing levels of authority and dignity: the metropolitical church, the primatial church, and the patriarchal church, each of which govern all cathedrals and other churches lower in the hierarchy within their jurisdiction.

Though cathedrals do not have to be elaborate buildings, many are, as they are often built to suggest visually the power and glory of the church. Cathedrals are therefore among the largest, most beautiful, and most visited church buildings in the world, and typically a major landmark in the cities they occupy.