**Core Concept**
The atlanto-axial joint is a synovial joint located in the cervical spine, specifically between the first and second cervical vertebrae (C1, or the atlas, and C2, or the axis). It allows for rotational movement of the head, enabling nodding and turning of the neck.

**Why the Correct Answer is Right**
The atlanto-axial joint is a pivot joint, where the odontoid process of the axis (C2) rotates within the ring of the atlas (C1). This unique joint is stabilized by the transverse ligament of the atlas, which prevents excessive movement. The joint capsule and the ligaments surrounding the joint also contribute to its stability. The rotation at this joint is facilitated by the articular surfaces of the atlas and axis, which are shaped to accommodate the movement.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the atlanto-axial joint is not a ball-and-socket joint, which is characterized by a spherical articular surface.
**Option B:** This option is incorrect because the atlanto-ocipital joint is located between the atlas (C1) and the occipital bone of the skull, and it allows for flexion and extension of the head, not rotation.

**Clinical Pearl / High-Yield Fact**
The atlanto-axial joint is a common site of injury in patients with Down syndrome, as the joint capsule and ligaments may be lax. This increases the risk of atlanto-axial instability and potential spinal cord injury.

**Correct Answer: C. Pivot joint.**