tracery

Etymology

trace + -ery

noun

1. (architecture) Bars or ribs, usually of stone or wood, or other material, that subdivide an opening or stand in relief against a door or wall as an ornamental feature.
   Because of the flamelike undulations of its window tracery, the Norman archæologist, M. de Caumont, who had brought into use the name Romanesque, invented the equally useful term Flamboyant. 1921, Elizabeth Boyle O'Reilly, How France Built Her Cathedrals, Harper & Brothers, page 140
2. (by extension) A delicate interlacing of lines reminiscent of the architectural ornament.