##### Basic Geometry Definitions

Segment Addition Postulate

Segment Addition Postulate

If B is between A and C, then AB + BC = AC

Undefined Terms in Geometry

Point

Line

Plane

Point

A point has no length or width, it just specifies an exact location

Line

A line is a straight one-dimensional figure having no thickness and extending infinitely in both directions.

Plane

In geometry, a plane is a flat two-dimensional "surface" (similar to a sheet of paper, but with no thickness and no finite length or width). A plane is defined by three points, each of which forms a line with the other two points within the plane.

Space

The set of all point

Collinear

Points that lie on the same line.

Non collinear

Points that are not all on the same line

Coplanar

a set of points in space is coplanar if all the points lie in the same geometric plane. For example, three distinct points are always coplanar; but a fourth point or more added in space can exist in another plane

Non coplanar

Not in the same plane

Ray

A ray is a part of a line that begins at a particular point (called the endpoint) and extends endlessly in one direction. A ray is also called half-line.

Ray

A ray is the part of the line which consists of the given point and the set of all points on one side of the end point.

Line Segment

A part of a line bounded by two end points