Plane
See It in Action
Two examples of the idea done right—and one common look-alike that is not right.
EXAMPLE
EXAMPLE
NON-EXAMPLE
Definition
In Geometry, a plane is another fundamental concept that is typically undefined but has an agreed-upon description.
A plane is a flat, two-dimensional surface that extends infinitely in all directions and has no thickness.
Key Characteristics:
It is made up of infinitely many points.
It has length and width, but no height (thickness).
It extends forever in all directions within its dimension.
A plane can be named using three non-collinear points (e.g., plane ABC) or a script capital letter (e.g., plane P).
Example:
If points A, B, and C are not on the same line (non-collinear), they define a unique plane — written as plane ABC.
In diagrams, a plane is often represented as a parallelogram or a shaded area, even though in reality, it has no edges and goes on infinitely.