a ray
It is a ray.
Angle
This is called a "ray". (It is equal to one half of a line.)
A line segment with the center of a circle as one endpoint and the other endpoint on the circumference of the circle is a rdius of that circle.
Half a straight line is called a "ray." A ray starts at a specific point, known as the endpoint, and extends infinitely in one direction. Unlike a line segment, which has two endpoints, a ray has only one endpoint and continues indefinitely.
parallel ~ Actually, all lines are straight and endless. A ray has one endpoint, is straight, and the other end of the ray is endless. A segment has a defined beginning and end, and is straight.
It has two endpoints. A ray has one endpoint.
Yes, a ray has only one endpoint.
a radius
A radius.
A ray has one endpoint and continues in the other direction infinitely.
It is a ray.