A line which divides a shape in two is called a bisector.
It is the midpoint of a line segment
This would be known as the Equator
When a ray divides an angle(Which is formed by 2 straight lines) in half that is equally on both the sides, it is termed as Angle Bisector.
That is the correct spelling of "bisect" (to divide equally in half, as in geometry).
Symmetry
to cut something in half equally
Half a circle is called a "semicircle" in geometry.
The lower quartile divides the lower half into two equal parts.
A bisector divides an angle in half (usually in the form of a line passing through the centre of the angle).
the equator
The equator divides the earth into the north and south hemispheres.
It is 180 degrees
No. A diameter divides a circle in half. A radius is half the diameter.