tracery

noun

1. 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.”

2. (broadly)A delicate interlacing of lines reminiscent of the architectural ornament.

   “He is homesick for the hale rough weather; for the tracery of the frost upon his window-panes at morning, the reluctant descent of the first flakes, and the white roofs relieved against the sombre sky.”