This document defines basic geometric terms including points, lines, line segments, rays, angles, planes, and relationships between lines and angles. It provides definitions and examples of each term. Points have no dimensions, lines extend infinitely in both directions, line segments have two endpoints, rays have one endpoint, angles are formed by two intersecting rays and their vertex, planes extend infinitely, and relationships between lines include intersecting, parallel and perpendicular. Angle relationships include complementary, supplementary and vertical angles.

1. Basic Geometric Terms
Definition Example
Point – an exact location in space. A point has no
dimension.
(read “point A”)
Line – a collection of points along a straight path
that extends endlessly in both directions.
‫ܤܥ‬ശሬሬሬሬԦ (read “line CB”)
Line Segment – a part of a line having two
endpoints. ‫ܤܣ‬തതതത (read “line segment ‫)”ܤܣ‬
The length of ‫ܤܣ‬തതതത is denoted ‫.ܤܣ‬
Ray – a part of a line having only one endpoint.
‫ܦܥ‬ሬሬሬሬሬԦ (read “ray ‫)”ܦܥ‬
The endpoint is always the first letter.
Angle – consists of two rays that have a common
endpoint called the vertex of the angle.
‫ܥܤܣס‬ (read “angle ‫)”ܥܤܣ‬
The vertex is always the middle letter.
‫ܥܤܣס‬ can also be written as ‫ܣܤܥס‬ or just ‫.ܤס‬
Plane – a flat surface that extends endlessly in all
directions.
Plane ‫ܦܥܤܣ‬
Straight Angle – an angle whose measure is 180°.
‫ܥܤܣס‬ is a straight angle.
Right Angle – an angle whose measure is 90°.
‫ܨܧܦס‬ is a right angle.
A
C B
A B
C D
BA
C
Vertex
A
B C
D
A B C
D
E F
Symbol for
right angle

2. Acute Angle – an angle whose measure is less than
90°.
‫ܼܻܺס‬ is an acute angle.
Obtuse Angle – an angle whose measure is more
than 90° and less than 180°.
‫ܧܦܥס‬ is an obtuse angle.
Two angles are complementary if the sum of their
measures is 90°.
݉‫ܣס‬ ൅ ݉‫ܤס‬ ൌ 25° ൅ 65° ൌ 90°
‫ܣס‬ and ‫ܤס‬ are complementary angles.
Two angles are supplementary if the sum of their
measures is 180°.
݉‫ܥס‬ ൅ ݉‫ܦס‬ ൌ 40° ൅ 140° ൌ 180°
‫ܥס‬ and ‫ܦס‬ are supplementary angles.
Intersecting Lines – two lines that cross.
‫ܥܣ‬ശሬሬሬሬԦ intersects ‫ܧܦ‬ശሬሬሬሬԦ at point ‫.ܤ‬
Parallel Lines – two lines in the same plane that do
not intersect.
‫ܨܧ‬ശሬሬሬሬԦ ‫צ‬ ‫ܪܩ‬ശሬሬሬሬԦ is read “‫ܨܧ‬ശሬሬሬሬԦ is parallel to ‫ܪܩ‬ശሬሬሬሬԦ.”
Perpendicular Lines – two lines that intersect to
form right angles.
ܴܶശሬሬሬሬԦ ٣ ܲܳശሬሬሬሬԦ is read “ܴܶശሬሬሬሬԦ is perpendicular to ܲܳശሬሬሬሬԦ.”
‫,ܴܲܵס‬ ‫,ܴܳܵס‬ ‫,ܶܵܲס‬ and ‫ܶܵܳס‬ are all right angles.
Vertical Angles – two angles with equal measure
formed by two intersecting lines.
‫ܧܣܤס‬ and ‫ܥܣܦס‬ are vertical angles.
‫ܦܣܤס‬ and ‫ܥܣܧס‬ are vertical angles.
X
Y
Z
C
D E
A 25° B
65°
D
140°40°
C
A B
C
D
E
FE
G H
P Q
R
S
T
B
C
D
E
A
120°
120°
60° 60°