vesica piscis.
1. Glory, mandala, or mandorla of the upright almond-shaped type produced by the geometrical process of placing two equilateral triangles above and below a baseline as mirror-images and striking arcs from each end of the base-line passing through the other points of the triangle. This creates two pointed arches base-to-base, commonly found as a vertical aureole enclosing of figure of e.g. Christ in Majesty. Its resemblance to a fish, or to a fish's bladder, relates it to the Chrismon. The shape is also found in windows, e.g. the rose-window in the south transept of Lincoln Cathedral.

2. Light in Second Pointed Curvilinear or Flowing tracery resembling a tadpole or the air-bladder of a fish.

vesica piscis a pointed oval figure (also called mandorla) used as an architectural feature and as an aureole enclosing figures such as Christ or the Virgin Mary in medieval art. The term is Latin, and means literally ‘fish's bladder’; the reason for the name is not clear, although it may refer to the shape.