acute angle
An angle that measures less than a right angle (90°).
Example:
addend
Any of the numbers
that are added
Example:
2 + 3 = 5
The addends are 2
and 3.
angle
A figure formed by two rays that meet at a common
endpoint
Example:
area
The number of square units needed to cover a
given surface
Example:
The area is 9 square
units.
array
An arrangement that shows
objects in rows and columns
Example:
average
One way to find a number
that best represents all the
numbers in a set
Example:
bar graph
A way to show information
that uses bars to stand for data
Example:
centimeter (cm)
A unit of length
in the metric system
100 centimeters = 1 meter
circle graph
A graph in the shape of a circle that shows data as a whole made up of
different parts
Example:
closed figure
A shape that begins and
ends
at the same point
Examples:
congruent figures
Figures that have
the same size and shape
Example:
The triangles are
congruent.
cube
A solid figure with six
Examples:
cylinder
A solid figure that is
shaped like a can
Examples:
decimal
A number that uses place value and a decimal point to show values
less than one, such as tenths
and hundredths
Example:
3.47
decimal point
A period used in decimal numbers to separate
the whole number part
from the decimal part
Example:
decimeter (dm)
A unit of length
in the metric system
10 centimeters = 1
decimeter
degree
A unit of measure used to
measure parts of a circle.
There are 360° in a
circle.
Example:
denominator
The number below the bar
in a fraction. It tells the
total number of equal parts.
Example:
diameter
A line segment that passes through
the center
of a circle and has its
endpoints on the circle
Example:
difference
The answer
in a subtraction problem
Example:
8 - 5 = 3
3 is the difference.
dividend
The number that is being
divided in a division problem
Examples:
35 ÷ 5 = 7
The dividend is 35.
divisor
The number that
Examples:
18 ÷ 3 = 6 
The divisor is 3.
double-bar graph
A graph using bars to compare similar kinds of
data.
Example:
elapsed time
The time that passes
from the start of an
activity
to the end of it.
Example:
The elapsed time is one
hour.
equation
A number sentence
that uses an = to show
that 2 amounts are equal.
Examples:
9 – 3 = 6
n + 7 = 15
equilateral triangle
A triangle with all sides congruent
Example:
equivalent decimals
Two or more decimals that name the same
amount
Example:
0.3 = 0.30
equivalent fractions
Two or more fractions that name the same
amount
Example:
expanded form
A way to write numbers by
showing the value of each digit
Examples:
635 = 600 +
30 + 5
1,479 =
1,000 + 400 + 70 + 9
expression
A part of a number
sentence that combines
numbers and operation
signs
Example:
(12 – 4) – 3
fact family
A set of related addition and
and division number sentences
Examples:
2 + 4 = 6
6 - 4 = 2
4 + 2 = 6 6 - 2 = 4
3 X 6 = 18
18 ÷ 6 = 3
6 X 3 = 18 18 ÷ 3 = 6
factor
A number that is multiplied
by another number
to find a product
|
4 |
|
|
4
X 7 =
28 |
X
7 |
|
28 |
|
The factors
are 4 and 7.
foot (ft)
A unit of length in the customary system
12 inches = 1 foot
fraction
A number that names part
of a whole or part of a group
Example:
hexagon
A polygon with 6 sides
and 6 angles
Examples:
horizontal
The direction from left to
right
horizontal
hundredth
One of one hundred equal
parts
Example:
inch (in.)
A unit of length in the customary system
12 inches = 1 foot
intersecting lines
Two or more lines that
cross at exactly one point
Example:
The lines intersect at
point B
inverse operations
Opposite operations that
undo each other; Addition and
subtraction are
inverse operations, and so
are multiplication and division.
Examples:
5 + 4 = 9, so 9 – 4 = 5
3 X 4 = 12, so 12 ÷ 4 = 3
isosceles triangle
A triangle with
two congruent sides
Example:
less than (<)
A symbol used to compare
two numbers, with the
lesser number given first
Example:
6 < 8
6 is less than 8.
line
A straight path extending
in both directions with no endpoints
Example:
line AB or line BA
line graph
A graph that uses line segments to show how data change over a period of
time
Example:
line plot
A diagram that shows
Example:
line segment
Part of a line, with two endpoints
Example:
line symmetry
A figure has line symmetry
when it can be folded so that
its two parts are
identical
Example:
median
The middle number in an
ordered series of numbers
Example:
The median of 1, 3, 4, 6,
and 7 is 4.
meter (m)
A unit of length
in the metric system
100 centimeters = 1 meter
mile (mi)
A unit of length in the customary system
5,280 feet = 1 mile
mixed number
A number that is made up
of a whole number and a fraction
Example:
|
2 |
1 |
|
2 |
mode
The number that occurs
most often in a list of data
Example:
The mode of 1, 3, 4, 4,
and 6 is 4.
multiple
A number that is the product
of 2 numbers
Example:
negative numbers
Numbers less than zero
Example:
numerator
The number above the bar
in a fraction. It tells how
many of the equal parts of the whole or group are being considered.
Example:
obtuse angle
An angle whose measure is greater
than 90°
and less than 180°
Example:
octagon
A polygon with
8 sides and 8 angles
Examples:
one-dimensional
A measure in only one
direction, such as length
Examples:
open figure
A shape that does not
begin and end at the same point
Examples:
ordered pair
A pair of numbers used to
locate a point on a grid. The 1st number tells the
left-right position &
the 2nd number
tells the up-down
position.
Example:
(1,2)
ounce (oz)
A customary unit used to measure
weight
16 ounces = 1 pound
parallel lines
Lines that stay exactly
the same distance apart
Example:
parallelogram
A quadrilateral whose opposite
sides are parallel and congruent
Examples:
partial product
A method of multiplying where the ones, tens,
hundreds,
and so on are multiplied
separately and
then the products added together
Example:
pentagon
A polygon with 5 sides
and 5 angles
Examples:
perimeter
The distance around a
figure
Example:
2 cm + 3 cm + 3 cm = 8 cm
pictograph
A graph that uses pictures
to show and compare information
Example:
place value
The system in which the
position of a digit in a number determines its value
Example:
point
The name of a location on
an object and in space
Example:
. A
point symmetry
When a figure can be
turned about a central point
& still look the same
in at least 2 positions
Example:
polygon
A closed plane figure with straight sides
Examples:
pound (lb)
A customary unit used to measure
weight
16 ounces = 1 pound
probability
The chance that a
given event will occur
Example:
|
Probability of red = |
1 |
|
4 |
product
The answer to a
multiplication problem
Example:
6 X 2 = 12
The product is 12.
quadrilateral
A polygon with four
angles and four sides
Examples:
quotient
The answer in a division problem
Examples:
35 ÷ 5 = 7 
The quotient is 7.
radius
A line segment with one endpoint at
the center of a circle & the other on the circle
Example:
range
The difference between the greatest
and the least
in a set of numbers
range: 6 – 0 = 6
ray
A part of a line that begins at one endpoint
and extends forever in only one direction
rectangle
A polygon with 4 sides and 4 right angles
Example:
rectangular prism
A solid figure in which all six faces are rectangles
Example:
remainder
The amount left over
when you find a quotient
Example:
rhombus
A parallelogram whose four sides
are congruent & whose
opposite angles are congruent
Example:
right angle
An angle that forms a square corner
and measures 90°
Example:
rotation (turn)
The action of turning a
figure around a point or a vertex
Example:
scalene triangle
A triangle in which each side
has a different length
Example:
similar figures
Figures that have the same
shape
but may have different
sizes
Example:
simplest form
When a fraction can be
modeled with the largest
fraction bar possible
Example:
solid figure
Examples:
|
sphere |
|
cube |
|
cylinder |
rectangular |
|
|
cone |
square |
square
A polygon with 4 equal sides
and 4 right angles
Example:
square pyramid
A solid figure with a base
that is a square and
Example:
standard form
A way to write numbers
by using digits
Example:
3,023
sum
The answer to an addition
problem
Example:
12 + 7 = 19
The sum is 19.
tally table
A way to organize data that uses tally marks to show how often
something happens
Example:
tangram
A puzzle consisting of
seven polygon-shaped pieces
that
can be rearranged to make
various figures or shapes
tenth
One of ten equal parts
Example:
three-dimensional
A measure in three
directions, such as length, width, and height
Examples:
trapezoid
A quadrilateral with only
one pair of parallel sides
Example:
triangle
A polygon with 3 sides
and 3 angles
Examples:
two-dimensional
A measure in two
directions, such as length and width
Examples:
variable
A letter that can stand
for any number
Example:
vertex
The point at which two rays of an angle or two or more
line segments meet
Examples:
vertical
The direction from
top to bottom
Example:
volume
The measure of the space a
solid figure occupies
Example:
written form
A way to write numbers
by using words
Example:
two-hundred fifty-seven
x-coordinate
The first number
in an ordered pair
Example:
(4, 6) (2, 5)
yard (yd)
A unit of length in the customary system
1 yard = 3 feet
y-coordinate
The second number in an ordered pair
Example:
(3, 7) (5, 9)