8th Grade Math Vocabulary: Terms and Definitions

In 8th grade, you'll be introduced to new math terms that relate to algebra, geometry and statistics, as well as the number system. Keep reading to learn new 8th grade math vocabulary!

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Math Terms for 8th Grade

The Number System

Rational number
A number that can be written as a fraction. Rational numbers include integers and fractions, as well as many decimals and radicals.
Irrational number
Numbers that cannot be written as fractions. Examples of irrational numbers include pi, radical two and Euler's number.


Cube root
When a number, n, is cubed, and it produces another number, x, then n is the cube root of x (n^3 = x). For instance, (cube root of 27) = 3 because 3^3 = 3 x 3 x 3 = 27.
Scientific notation
A shorthand method for writing very small or very large numbers using positive and negative powers of ten. For example, 7,000,000 can be written as 7.0 x 10^6, and 0.00007 is written as 7.0 x 10^-5.
The steepness of a line on a graph. It is calculated by the change in y divided by the change in x between two coordinate points (x, y) on the line. When an equation is in slope-intercept form, slope is represented by the variable m.
Unit rate
The amount of change in one variable produced by a unit of change in another variable. Examples of unit rates include cost per unit and miles or kilometers per hour.


Two shapes are congruent if their corresponding sides and angles are all equal.
A shape is similar to another shape if its sides and angles are all proportional to the corresponding sides and angles of the other shape.
Pythagorean Theorem
This theorem addresses the connection between a right triangle's hypotenuse, c, and its other two sides, a and b. The theorem is a^2 + b^2 = c^2.

Statistics and Probability

Categorical data
Data relating to a variable that places the population into different groups, such as race or geographic location.
Bivariate data
A set of data that contains information about two variables, such as annual income and education level for individuals.
A graph that displays bivariate data so that each member of the population is represented by a dot. By looking at the overall pattern of dots on the graph, you can get a general idea about the relationship between the two variables.
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