Undefined Terms
A word that does not have a formal definition, but there is agreement about what the word means. Example: Point, Line, Plane.
Point
A point has no dimension. It is usually represented by a dot.
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.
Collinear Points
Points that lie on the same line.
Coplanar Points
Points that lie in the same plane.
Defined Terms
Terms that can be described using known words. Example: Ray, Line Segment, Angle.
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.
Ray
Part of a line that consists of one point called an endpoint and all points on the line that extend in one direction.
Opposite Rays
Rays that share an endpoint, but extend in opposite directions.
Intersection
The set of points that two or more geometric figures (line or plane, for example) have in common.
Congruent Segments
Line segments that have the same length.
Midpoint
A point that divides, or bisects, a segment into two congruent segments.
Between
When three points are on a line, you can say that the point in the middle, is between the other two points.
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.
Segment Bisector
A point, line, ray, segment, or plane that intersects a segment at it's midpoint.