In geometry, there are three fundamental concepts that are considered undefined terms. These terms are the building blocks for defining other geometric concepts and figures. The three undefined terms are:
- Point: A point is a location in space that has no size, no width, no length, and no depth. It is represented by a dot and named using a capital letter.
- Line: A line is a straight one-dimensional figure that extends infinitely in both directions. It has no thickness and is named using two points on the line or a lowercase letter.
- Plane: A plane is a flat, two-dimensional surface that extends infinitely in all directions. It has no thickness and is named using three points on the plane or a capital letter.
These undefined terms are essential because they help define other geometric terms and concepts. For example, a line segment is defined as part of a line between two points, and an angle is formed by two rays with a common endpoint.