Points, Lines, and Planes Vocabulary

Line

A line has one dimension. It is usually represented by a straight line with two arrowheads to indicate that the line extends without end in two directions.

Plane

A plane has two dimensions. It is usually represented by a rhombus. A plane extends without end, even though the drawing appears to have edges.

Point

A point has no dimension. It is usually represented by a dot.

Midpoint

A point that divides, or bisects, a segment into two congruent segments.

Segment Bisector

A point, line, ray, segment, or plane that intersects a segment at it's midpoint.

Undefined Terms

A word that does not have a formal definition, but there is agreement about what the word means. Example: Point, Line, Plane.

Congruent Segments

Line segments that have the same length.

Ray

Part of a line that consists of one point called an endpoint and all points on the line that extend in one direction.

Line Segment

Part of a line that consists of two points, called endpoints, and all points on the line that are between the endpoints.

Endpoints

Points that are designated ends of a line segment or end of a ray.

Coplanar Points

Points that lie in the same plane.

Collinear Points

Points that lie on the same line.

Opposite Rays

Rays that share an endpoint, but extend in opposite directions.

Defined Terms

Terms that can be described using known words. Example: Ray, Line Segment, Angle.

Distance

The absolute value of the difference between the coordinates of two points.

Coordinate

The real number that corresponds to a point on a line.

Intersection

The set of points that two or more geometric figures (line or plane, for example) have in common.

Between

When three points are on a line, you can say that the point in the middle, is between the other two points.