Tracery

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.
2. A delicate interlacing of lines reminding of the architectural ornament.
• 1881, , :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.