Tracery
Tracery is the pattern of stone ribs and bars that divides the upper part of a Gothic window into shapes. Early tracery was made by cutting holes in a stone slab, known as plate tracery. Later, thin stone bars were curved into foils, circles and flowing shapes, which is called bar tracery. The glass is set between the bars.
The style of the tracery is one of the easiest ways to date a church window. Geometric patterns of circles and cusped shapes belong to the thirteenth century, flowing curves to the fourteenth, and the upright grid of panels typical of the Perpendicular style to the fifteenth and early sixteenth centuries.
Each shape in the tracery is called a light or a tracery light, and each was often given its own small figure, symbol or angel.