A flattened or shallow articulating surface of a bone?

A flattened or shallow articulating surface of a bone is referred to as a "facet." Facets are typically found on the surfaces of bones that come into contact with one another at joints, allowing for smooth movement and reducing friction. These surfaces can be found in various joints, such as the vertebrae in the spine, where facets help facilitate flexion and rotation. The design of facets contributes to the stability and range of motion of the joint.