What is half a circle called in geometry?

In geometry, the half circle is referred to as the semicircle. The semicircle is made by dividing a whole circle along its diameter. Alternatively, a semicircle could also be an open arc where a curved line represents half a circle's circumference but with no straight diameter line closing its area.

A semicircle's area is always half the area of the original circle that is divided. To measure the area of a semicircle, pi needs to be multiplied to the square of the semicircle's radius before being divided into two. The perimeter of the semicircle is measured by adding the multiplication result of pi with the radius of the semicircle and twice the radius of the semicircle.