The only defined term of those listed is:

line
angle
plane
point

angle.

The only defined term among those listed is a point.

To determine the only defined term among "line," "angle," "plane," and "point," we need to understand the definitions of these geometric terms:

1. Line: A line is a straight path with no thickness or width that extends infinitely in both directions.

2. Angle: An angle is formed when two rays share a common endpoint called a vertex. It is typically measured in degrees or radians and is used to describe the amount of rotation between the rays.

3. Plane: A plane is a flat, two-dimensional surface that extends infinitely in all directions. It has no edges or boundaries.

4. Point: A point is a location in space that has no size or dimension. It is represented by a dot and is often used as a reference to describe the location of other geometric figures.

Now, examining these definitions, we can conclude that "point" is the only defined term among the options given. While each term has its own definition, the other terms (line, angle, and plane) are composed of points and therefore rely on the concept of a point to be defined.