bossage

from The Century Dictionary.

• noun In building: A stone which projects beyond the face of the adjacent work, and is laid rough, to be afterward carved into some ornamental or significant form.
• noun Rustic work, consisting of stones which advance beyond the face of the building, with indentures or channels left in the joinings: used chiefly upon projecting corners.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arch.) A stone in a building, left rough and projecting, to be afterward carved into shape.
• noun (Arch.) Rustic work, consisting of stones which seem to advance beyond the level of the building, by reason of indentures or channels left in the joinings.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun architecture A rough, unfinished stone block, which is left projecting from the wall of a building to be later sculpted.