Final answer:
An archivolt is the decorative molding or band on the face of an arch, following the curve of the intrados and is distinct from the keystone, which is the central stone that locks the arch together.
Step-by-step explanation:
The decorative molding or band on the face of an arch that follows the curve of the intrados is known as an archivolt. This element is a characteristic feature in Romanesque and Gothic architecture. The archivolt often features sculpted or engraved patterns and is made up of several voussoirs, the wedge-shaped stones that construct the arch. While the keystone is the central voussoir that locks all the other voussoirs into place, completing the arch structure and enabling it to bear weight, the archivolt refers specifically to the ornamental aspect that follows the arch's curve.