A sector.
It is the subtended angle of the arc
A quarter of a circle, formed by two radii forming a right angle at the centre, is called a quadrant.
A detripage
We call it a "semi-circle"
A semi-circle
Concentric Circles?
We call it a circle.
A circle with three dimensions is sphere.
a semi circle? common sense
Inscribed
A quarter of a circle or a quadrant!
The perimeter of a circle is called the circumference