As you can see from the figure above, a sector is a pie-shaped part of a circle. It has two straight sides (the two radius lines), the curved edge defined by the arc, and touches the center of the circle.
|Radius||The radius of the circle of which the sector is a part|
|Central Angle||The angle subtended by the sector to the center of the circle. See Central Angle of an Arc for more.|
|Arc length||The length around the curved arc that defines the sector (shown in red here). For more on this see Arc length definition.|