Apse - Oxford Definition

Usually a circular or multi-angular termination of a church at its eastern end, first found in Roman basilicas, with a rounded vault above. The apse was mainly a Continental development, whereas English Gothic churches tended to have square terminations. However, in the increasingly subtle and complex spatial development of later Gothic architecture apses are found in chancel-aisles or even as chapels on the east sides of transepts (Lincoln Cathedral).