Point
A location represented by a dot

Line
An infinate set of points extending endlessly in both directions

Plane
Set of points that form a flat surface that extends infinitely in both directions

Collinear
Points that are on the same line

Non-collinear
Points that are not on the same line

Betweenness
B is between A and C if and only if A, B, C are distinct collinear points and AB + BC = AC

Coplanar
Points that are on the same plane

Parallel Lines
2 lines that never intersect (in same plane)

Perpendicular Lines
2 lines that intersect to form right angles (in same plane)

Line segment
Set of points consisting of two points on a line, called endpoints , and all points on the line between the endpoints

Length/Measure of a Segment
Distance between its endpoints

Congruent Segments
Segments that have the same length/measure

Midpoint
Point on a segment that divides the segments into 2 congruent segments

Bisector of a Segment
Line, ray or a segment that intersects a segment at its midpoint

Ray
Part of a line consisting of an endpoint and extending infinitely in the other direction

Opposite Rays
2 rays of the SAME LINE with a common endpoint.

Angle
The union of 2 rays having the same endpoint (vertex)

Straight Angle
A 180 degree angle (line)

Acute Angle
Between 0 degrees and 90 degrees

Right Angle
A 90 degree angle

Obtuse Angle
between 90 degrees and 180 degrees

Congruent Angles
Two angles that have the same measure

Angle Bisector
Ray whose endpoint is the vertex of the angle and it divides the angle into 2 congruent angles

Complementary Angles
A pair of angles, the sum of whose degree measures 90 degrees

Supplementary Angles
A pair of angles, the sum of whose degree measures 180

Linear Pair
2 adjacent angles whose sum is a straight angle

Vertical Angles
Angles formed across from one another and are congruent

Adjacent Angles
Two angles who share a common vertex, common side (ray), but no common interior points

Polygon
A closed figure in a plane that is the union of line segments such that the segments only intersect at their endpoints and no segments sharing a common endpoint are collinear.

Triangle
A polygon that has exactly 3 sides

Scalene triangle
Triangle that has exactly had no cogruent sides

Isosceles Triangle
Triangle that has 2 congruent sides

Equilateral Triangle
Triangle that has 3 congruent sides

Acute Triangle
Triangle that has 3 acute angles

Equiangular Triangle
Triangle that has 3 congruent angles

Right Triangle
Triangle that has a right angle

Obtuse Triangle
Triangle that has an obtuse angle

Parallel Lines
Lines in the same plane that have no points in common OR all points in common.

Altitude
(height) Line segment drawn from a vertex to the opposite side and is perpendicular to it.

Median
Line segment drawn from a vertex to the midpoint of the opposite side.

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