# Geometry Glossary

 Recommend this site on social media! To hear the sound, you need to allow the scripts on this page to load. Tweet

Geometry Glossary

A | | B | | C | | D | | E | | F | | G | | H | | I | | K | | L | | N | | O | | P | | Q | | R | | S | | T | | U | | V

# A

A
acute angle: an angle less than 90 degrees
angle: the space between two intersecting lines that share the same endpoint
apex: the point off the base of a pyramid where the triangular sides meet
area: the number of square units needed to completely cover a 2-d shape

# B

B
base: the bottom face of a solid

# C

C
circle: a perfectly round 2-d figure. All points on a circleâ€™s outline (the circumference) are the same distance from the centre.
circumference: the perimeter of a circle
clockwise rotation: turning in the same direction as the hands of a clock around a clock face
compass: a tool for drawing circles
complementary angles: two angles that measure 90 degrees in total
cone:a 3-d solid with one circular base, and one vertex (apex), and a curved surface all around
congruent shapes: geometric shapes that have the same size and shape
counterclockwise: opposite of clockwise
cube: a special rectangular prism made of 6 equal squares
curve, curved: bent not straight as in the outline of circles or some surfaces found in cylinders, cones, etc.
cylinder: a solid shaped like a tube with two circular bases and a curved surface all around.

# D

D
decagon: a ten-sided polygon
degree: a unit for measuring the size of an angle (one full turn is 360 degree)
diameter: a straight line segment whose endpoints are on the circle and its middle is the centre of the circle
dodecagon: a twelve-sided polygon

# E

E
edge: the line on a 3-d solid where two faces meet
equilateral: refers to a polygon whose sides are equal in length (example: equilateral triangle)
equilateral triangle: a triangle with all sides equal

# F

F
face: a flat surface of a polyhedron surrounded by edges

# G

G
geoboard: a board with a number of pegs. Elastic bands are wrapped around the pegs to make polygons in order to study their properties (perimeter, area, angles, etc.)
geometry: a branch of mathematics that studies points, lines, angles, shapes, solids, etc.

# H

H
heptagon: a seven-sided polygon
hexagon: a six-sided polygon
hexagonal prism: a prism with 8 faces (2 hexagonal and 6 rectangular), 18 edges, and 12 vertices.
hexagonal pyramid: a pyramid with a hexagonal base and six triangular faces that meet at the apex.

# I

I
interior angles: angles on the inside of a shape
intersect: cross
intersecting lines: two different lines that cross one another and share only one point (at their intersection)
isometric dot paper: a paper with dots that are equally spaced apart
isosceles triangle: a triangle with two equal sides

# K

K
kite: a quadrilateral with 2 pairs of equal sides. Each pair is adjacent (side by side and sharing a point)

# L

L
line of reflection: a line used to reflect or flip a shape
line of symmetry: a central dividing line that creates two congruent halves, which are reflection of each other

# N

N
net: an outline that can be folded up to build a 3-d model of a solid
nonagon: an nine-sided shape

# O

O
obtuse angle: an angle that measures between 90 and 180 degrees
octagon: an eight-sided shape
octagonal prism: a solid with 10 faces (2 octagonal and 8 rectangular), 24 edges, and 16 vertices.
octagonal pyramid: a pyramid with 1 octagonal base and 8 triangular faces that meet at the apex.
oval: a round shape that looks like a circle that has been stretched

# P

P
parallel lines: lines that run side by side and never intersect nor get closer or farther
parallelogram: a quadrilateral whose opposite sides are parallel
pentagon: a five-sided shape
pentagonal prism: a solid with 7 faces (2 pentagonal and 5 rectangular), 15 edges, and 10 vertices.
pentagonal pyramid: a pyramid with a pentagonal base and five triangular faces that meet at the apex.
perimeter: the distance around a closed shape
perpendicular: at right angles, forming a 90 degrees angle
polygon: a closed shape that is made of at least 3 side
polyhedron: a 3-d solid with polygons as its faces
prism: a solid with two congruent, parallel bases and rectangular sides
protractor: a tool for measuring angles
pyramid: a solid that has one base and a set of triangles as its sides, which slope to meet at a single point (apex) above the base

Q

# R

R
radius: the distance between the center of a circle and any point on the circle
rectangle: a quadrilateral which has 4 right angles
rectangular prism: a solid with 6 rectangular faces, 12 edges, and 8 vertices.
rectangular pyramid: a pyramid with a rectangular base and four triangular faces that meet at the apex.
reflection: flip
reflex angle: an angle greater than 180 degrees, but less than 360
reflex vertex: a vertex of a polygon that forms an interior angle greater than 180 degrees
regular polygon: a polygon whose sides and angles are all equal (e.g., square)
rhombus: a parallelogram with four equal sides
right angle: a 90 degrees angle
right triangle: a triangle that has a right angle
right trapezoid: a trapezoid with two right angles
rotation: turn

# S

S
scalene triangle: a triangle with no equal sides
semicircle: half of a circle
sphere: a 3-d solid that looks like a ball
square: a special quadrilateral with 4 equal sides and 4 right angles
square pyramid: a pyramid with a square base and four triangular faces that meet at the apex.
straight angle: an angle that measures180 degrees
supplementary angles: two angles that measure 180 degrees in total
symmetrical: a shape having two halves which are mirror images of each other

# T

T
tessellation: a repeating pattern of shapes that cover a surface without overlapping the shapes or leaving any gaps
translation: slide
trapezoid: a quadrilateral that has only one pair of parallel sides
triangle: a three-sided polygon
triangular prism: a solid with 5 faces (2 triangular and 3 rectangular), 9 edges, and 6 vertices.
triangular pyramid: a pyramid with 4 triangular faces, 6 edges and 4 vertices.

# U

U
undecagon (also called hendecagon): an eleven-sided shape

# V

V
vertex: the point where two sides of a polygon meet, or the point where three or more edges of a polyhedron meet
vertices: more than one vertex