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In architecture, a piercing or panel divided by cusps or foliations into four leaves, or more correctly the leaf shaped figure formed by the cusps. It is supposed to represent the four leaves of a cruciform plant.

Quatrefoil

In architecture, a piercing or panel divided by cusps or foliations into four leaves, or more correctly…

The transept is the area set crosswise to the nave in a cruciform ("cross-shaped") building in Romanesque and Gothic Christian church architecture. The transept separates the nave from the sanctuary, whether apse, choir, chevet, presbytery or chancel. The transepts cross the nave at the crossing, which belongs equally to the main nave axis and to the transept.

One Bay of Transept, Winchester Cathedral

The transept is the area set crosswise to the nave in a cruciform ("cross-shaped") building in Romanesque…