1. The problem asks to identify the highlighted part of circle O, where O is the center of the circle and the shaded region is between points O and S. 2. In circle geometry, a **sector** is the region bounded by two radii and the arc between them. 3. Since the shaded part is between point O (center) and point S on the circle, it is formed by two radii and the arc between them. 4. This means the highlighted part is a **sector** of the circle. 5. The term **central angle** refers to the angle formed at the center of the circle by two radii, which also defines the sector. 6. Therefore, the highlighted part is the **sector** defined by the **central angle** at O. Final answer: The highlighted part is the **O central angle** (sector of the circle).