acute angle
An angle that measures less than 90 degrees.

A figure made up of two rays that share the same endpoint.

common denominator
The same denominator in two or more fractions. For instance, \(\frac{1}{4}\) and \(\frac{5}{4}\) have a common denominator.

composite number
A whole number with more than 1 factor pair.

The bottom part of a fraction that tells how many equal parts the whole was partitioned into.

The number being divided. For example, when 37 is divided by 5, we call 37 the dividend. 

equivalent fractions
Fractions that have the same size and describe the same point on the number line. For example, \(\frac{1}{2}\) and \(\frac{2}{4}\) are equivalent fractions.

factor pair of a whole number
A pair of whole numbers that multiply to result in that number. For example, 5 and 4 are a factor pair of 20.

intersecting lines
Lines that cross.


A set of points that are arranged in a straight way and extend infinitely in opposite directions.

line of symmetry
A line that divides a figure into two halves that match up exactly when the figure is folded along the line.

mixed number
A number expressed as a whole number and a fraction less than 1. 

multiple of a number
The result of multiplying that number by a whole number. For example, 18 is a multiple of 3, because it is a result of multiplying 3 by 6.


The top part of a fraction that tells how many of the equal parts are being described.

obtuse angle
An angle that measures greater than 90 degrees.

parallel lines
Lines that never intersect.

perpendicular lines
Lines that intersect creating right angles.


A location along a line or in space.

prime number
A whole number that is greater than 1 and has exactly one factor pair: the number itself and 1.

A line that ends at one point and goes on in the other direction.

The number left over when we take away as many equal groups as we can from a number. 

right angle
An angle with a measurement of 90 degrees.

right triangle
A triangle with a 90 degree angle.


A formal way to say which number a given number is closer to. For example, for 182, the number 180 is the closest multiple of ten and 200 is the closest multiple of a hundred. We can round 182 to 180 (if rounding to the nearest ten) or 200 (if rounding to the nearest hundred).

segment or line segment

A part of a line with two endpoints.

straight angle
An angle that measures 180 degrees.

A figure has symmetry if its parts can match up exactly when the figure is folded or rotated.

The point where the two rays meet.