Detail of the stone vault in the staircase to the Refectory of Christ Church College, Oxford, 1847, Photo by Fr Lawrence Lew, O.P. via Flickr, Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic License. Detail of the stone vault in the staircase to the Refectory of Christ Church College, Oxford, 1847, Photo by Fr Lawrence Lew, O.P. via Flickr, Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic License.

Just a Second: Tracery

Tracery (noun)

Ornamental interlacing and branching lines in architecture.

Sometimes tracery is openwork decorating a window as in Gothic cathedrals and other times it spreads across flat surfaces like ceiling vaults.  Tracery can be carved in wood or made from brick, but most often it is created in stone.