A. Point

An exact location in space.

B. Line

A straight path that extends without
end in opposite directions.

C. Plane

A flat surface that extends forever.


D. Ray

A part of a line that starts at one endpoint
and extends forever.

E. Segment

A part of a line between two
endpoints.


F. Acute angle

An angle that measures less than
90 degree.


G. Right Angle

An angle that measures 90 degree.


H. Obtuse Angle

An angle whose measure is greater than
90 degree but less than 180 degree.


I. Complementary angles

Two angles whose measures add
to 90 degree.


J. Supplementary angles

Two angles whose measures have
a sum of 180 degree.


K. Straight angle

An angle that measures 180 degree.


L. Parallel lines

Lines in a plane that do not intersect.



M. Transversal

A line that intersects two or more lines.


N. Perpendicular lines

Lines that intersect to form right angles.


O. Vertical angles

A pair of opposite congruent angles formed by
intersecting lines.


P. Skew lines

Lines that lie in different planes that are neither 
parallel nor intersecting.


Q. Acute triangle

A triangle with all angles measuring
less than 90 degree.


R. Obtuse triangle

A triangle containing one obtuse triangle.


S. Isosceles triangle

A triangle with at least two congruent
sides.

T. Equilateral Triangle

A triangle with three congruent
sides.


U. Scalene Triangle

A triangle with no congruent sides.


V. Rectangle

A parallelogram with four
right angles.


W. Parallelogram

A quadrilateral with two pairs of
parallel sides.


X. Rhombus

A parallelogram with all sides
congruent.


Y. Square

A rectangle with four congruent
sides.