The distance covered by travelling once around a circle is its perimeter, usually called its circumference.

The portion (or part) of the circular region enclosed by two radii and the corresponding arc is called a sector of the circle.

The portion (or part) of the circular region enclosed between a chord and the corresponding arc is called a segment of the circle

Shaded region OAPB is a sector of the circle with centre O. ∠ AOB is called the angle of the sector.

In figure, unshaded region AQB is another segment of the circle formed by the chord AB. For obvious reasons, APB is called the minor segment and AQB is called the major segment.

In figure, AB is a chord of the circle with centre O. So, shaded region APB is a segment of the circle. unshaded region AQB is another segment of the circle formed by the chord AB. For obvious reasons, APB is called the minor segment and AQB is called the major segment.