It is a horizontal line segment.
A Dowel screw.
a straight angle
A line segment with a finite, non-zero gradient.
it's what you call circle
Line Segment
The vertex (or apex).
A ray. Rays have a starting point and no ending. They go on forever.
Abyssal plains
Well, darling, that's what we call a "ray". It's like a line that decided to show off and grow a pointy edge on both sides. So, next time you see a line feeling fancy with arrows, just remember it's called a ray.
The end would be called a point or an endpoint. It only has one end since it is infinite in the other direction.
The Camera?
line segment