Read two segments that are each half a circle.

What is the chord called?

What is the arc called?

A segment bounded by a diameter and a semi-circumference is a “semicircle.”

A semicircle is half a circle.

Read four segments each larger than a semicircle.

The part of the circle between the two radii o f, o i, and the arc f i, is called a “sector.”

Read four sectors each less than one-fourth of a circle.[[2]]

[2]. Thus, a sector bounded by the two radii o g, o h, and the arc g h.

A sector is a part of a circle bounded by two radii and an arc.