Question

which undefined term is used to define an angle?
line
plane
point
ray

Explanation:

An angle is defined as the union of two non - collinear rays with a common endpoint. A ray is an undefined term in geometry (part of the sub - field Geometry in Mathematics). A line is a straight path that extends infinitely in both directions. A plane is a flat, two - dimensional surface that extends infinitely. A point is a location in space. Since an angle is made up of rays (with a common vertex), the undefined term used to define an angle is a ray.

Answer:

ray