The first image shows a shaded region between the arc and the chord created by the same central angle. This shaded region is called segment.
The second image shows an arc intercepted by two radii of the circle. This arc is an intercepted arc.
The third image shows a shaded region corresponding to the entire region covered by a central angle. This region is called a sector.
The fourth image shows an angle originated at the center of the circle. This angle is a central angle.