Points, Lines and Planes are undefined terms in Geometry whose meaning is accepted without definition. These terms have similar meanings in Geometry as they are used in algebra, like the coordinate plane, ordered pairs and lines . Let us see the description of these terms and how they are represented.

Description
Representation Diagram
A represents just a location and does not have a size.
 A point is represented by a dot and is named
using a capital letter. The Point is A is shown here.
 Point Introduction
 A line has no thickness and contains infinitely many points and it represents a straight path
extending in opposite directions.
 A line is represented by two points on the line,
like Line Introductionor What is Line. A line is also represented by a single lower case
letters like 'l'.
 Line Introduction
 A plane is a flat surface made up of infinitely many points extending in all direction without
thickness.
A plane can be represented by a capital letter like Plane X.
It can also be represented by three points
which do not lie on the same line like
Plane ABC.
 Plane Introduction


Now, let us learn about some special points, lines and planes.

Collinear Points: A collinear set of points is a set of points all of which lie on the same straight line.
Collinear Points

In the above diagram, the points A, B. C and D are all points lying on the line 'l'.

Two points are sufficient to determine a line. Hence we discuss collinearity of three or more points and not with two points.

Non-Collinear Points: A non collionear set of points is a set of three or more points that do not all lie on the same straight line.
Non-Collinear Points

Three non collinear points define a plane and they form the vertices of a triangle.
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