b
In the slope-intercept form of a line, y = mx + b, the letter b stands for the y-intercept: the point where the line crosses the y-axis. It is also often used for the base of a figure.
Back substitution
Solving a system of equations by finding one variable first, then putting its value back into an earlier equation to find the others.
Back-to-back stem-and-leaf plot
A stem-and-leaf plot that shares one stem column between two data sets, with one set's leaves on the left and the other's on the right.
Bar graph
A graph that uses bars of different lengths to compare data, amounts or sizes across categories.
Bar model
A drawing that uses rectangles of different lengths to show the parts and whole in a word problem; also called a tape diagram.
Bar notation
A bar drawn over one or more digits of a decimal to show that they repeat forever.
Base (exponent)
In a power, the base is the number that is multiplied by itself. The exponent tells how many times it is used as a factor.
Base (geometry)
The side or face of a figure from which its height is measured, used to find area or volume.
Base (percent)
In a percent problem, the base is the whole amount that you are taking a percent of.
Base angles
The two angles at the ends of the base of an isosceles triangle. They are always equal.
Base of a logarithm
The number that is raised to a power in a logarithm. In log₂ 8 = 3, the base is 2 because 2³ = 8.
Base ten blocks
Blocks that model place value: a small cube is 1, a rod is 10 and a flat is 100.
Base ten system
Our number system, in which each place is worth ten times the place to its right; also called the decimal system.
Bearing
A direction given as an angle measured clockwise from north, usually written with three digits, such as 060°.
BEDMAS / BIDMAS
Memory aids for the order of operations: Brackets, Exponents (or Indices), Division and Multiplication, Addition and Subtraction. Also known as PEMDAS.
Bell curve
The symmetric, bell-shaped graph of a normal distribution, with most values near the mean and fewer values far from it.
Benchmark fraction
A common fraction such as 0, ¼, ½, ¾ or 1 used as a reference point to estimate or compare other fractions.
Between
Greater than one value and less than another. The numbers between 2 and 6 satisfy 2 < x < 6.
Biannual
Happening twice a year.
Bias
A systematic error that pushes results in one direction, so they do not fairly represent the truth.
Biased sample
A sample that does not fairly represent the population, because some members were more likely to be chosen than others.
Biconditional
A statement of the form "p if and only if q", which is true when p and q are both true or both false. Written p ↔ q.
Bilateral symmetry
Symmetry in which a figure can be divided by one line into two halves that are mirror images.
Billion
One thousand million: 1,000,000,000, or 10⁹.
Bimodal
Describes a data set or distribution that has two modes, which shows up as two peaks on a graph.
Bin
One of the equal-width intervals that data are grouped into for a histogram; also called a class interval.
Binary number system
A base-2 number system that uses only the digits 0 and 1. Each place is worth twice the place to its right.
Binary operation
An operation that combines two numbers to produce one result, such as addition, subtraction, multiplication or division.
Binomial
A polynomial with exactly two terms, such as 3x + 5.
Binomial coefficient
The number of ways to choose k items from n, written C(n, k). These numbers form Pascal's triangle and are the coefficients in a binomial expansion.
Binomial distribution
The probability distribution of the number of successes in a fixed number of independent trials, each with the same probability of success.
Binomial theorem
A formula for expanding a power of a binomial, (a + b)ⁿ, using binomial coefficients.
Bisect
To divide something into two equal parts. A segment is often bisected with a compass and straightedge.
Bisector
A line, ray or segment that divides a segment or angle into two equal parts.
Bivariate data
Data that pairs two variables for each item, such as hours studied and test score, often shown on a scatter plot.
Borrowing
In subtraction, taking 1 from a higher place value and adding 10 to the next lower place so the digits can be subtracted; also called regrouping.
Boundary line
The line that separates the region of solutions from the non-solutions when graphing a linear inequality. It is dashed when the line itself is not included.
Bounds of integration
The numbers a and b in a definite integral ∫ₐᵇ f(x) dx that mark where the area under the curve starts and ends; also called limits of integration.
Box-and-whisker plot
A graph that shows the spread of data using five numbers: minimum, first quartile, median, third quartile and maximum; also called a box plot.
Braces
The symbols { } used to list the elements of a set, and sometimes as a third level of grouping in expressions.
Brackets
The symbols [ ] used to group parts of an expression, usually around parentheses, to show which operation to do first.
Branch (of a hyperbola)
One of the two separate, mirror-image curves that make up a hyperbola.
Breadth
The distance across a shape from side to side; another word for width.
Break-even point
The point where total cost equals total revenue, so there is neither profit nor loss. On a graph, it is where the cost and revenue lines cross.