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Some basic geometry concepts, words and notations that you would need to know are points, lines, line segments, midpoints, rays, planes and space. Related Topics:

More Geometry Lessons

We may think of a **point** as a "dot" on a piece of paper
or the pinpoint on a board. In geometry, we usually identify this
point with a number or letter. A point has no length, width, or
height - it just specifies an exact location. It is zero-dimensional.

Every point needs a name. To name a point, we can use a single capital letter. The following is a diagram of points *A*, *B*, and *M*:

We can use a **line** to connect two points on a sheet of paper. A line is one-dimensional. That is, a line has length, but no width
or height. In geometry, a line is perfectly straight and extends forever in both directions. A line is uniquely determined by two points.

Lines need names just like points do, so that we can refer to them easily. To name a line, pick any two points on the line.

The line passing through the points

AandB

is denoted by

A set of points that lie on the same line are said to be **collinear**.

Because the length of any line is infinite, we sometimes use parts of a line. A **line segment** connects two endpoints. A line
segment with two endpoints *A* and *B* is denoted by
.

A line segment can also be drawn as part of a line.

The midpoint of a segment divides the segment into two segments
of equal length. The diagram below shows the midpoint *M* of
the line segment
. Since *M* is the midpoint, we know that the lengths *AM
*= *MB.*

A **ray** is part of a line that extends without end in one direction. It starts from one endpoint and extends forever in one
direction.

A ray starting from point

Aand passing throughBis denoted by

Planes are two-dimensional. A plane has length and width, but no height, and extends infinitely on all sides. Planes are thought of as flat surfaces, like a tabletop. A plane is made up of an infinite amount of lines. Two-dimensional figures are called plane figures.

All the points and lines that lie on the same plane are said to be **coplanar**.

A plane

Space is the set of all points in the three dimensions - length, width and height. It is made up of an infinite number of planes. Figures in space are called solids.

Figures in space

The following video gives the definitions of a point, a line, a plane, and space, as well as the symbols that are used in Geometry to represent each figure.

General Angle Basics: Angle Characteristics - rays, vertex,

Angle Classification - acute angle, right angle, obtuse angle, Complementary and Supplementary Angles

Understanding basic ideas in geometry and how we represent them with symbols