Final answer:
In geometry, the defined term among the options is c. 'point,' which is an essential undefined concept that represents a specific location with no size, shape, or dimension.
Step-by-step explanation:
The term 'point' is considered a defined term in geometry. In Euclidean geometry, a point is a basic undefined concept that describes a location with no size, shape, or dimensions. It is typically represented by a dot and labeled with a capital letter. Points are fundamental units from which other geometric terms such as lines, angles, and planes are defined.
A line is understood to be a straight one-dimensional figure with no thickness and extends infinitely in both directions, defined by two points. An angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint called the vertex. Finally, a plane is imagined as a flat surface that extends infinitely in all directions and is defined by any three non-collinear points.
The other terms, such as angle, line, and plane, are constructed using points and lines, and hence are not themselves undefined terms but defined in relation to points and lines.