Sale price
The price of an item after a discount is taken off the regular price.
Sales tax
A tax added to the price of goods when they are bought, usually a percent of the price.
Sample
A part of a population chosen to collect data from, so you can draw conclusions about the whole population.
Sample space
The set of all possible outcomes of a probability experiment.
SAS congruence
Side-Angle-Side: two triangles are congruent if two sides and the angle between them are equal.
Scale
The ratio of a length on a map or drawing to the actual length it represents, such as 1 cm : 5 km.
Scale drawing
A drawing of an object with all lengths reduced or enlarged by the same scale.
Scale factor
The number every length is multiplied by to enlarge or reduce a figure.
Scalene triangle
A triangle with no equal sides and no equal angles.
Scatter plot
A graph of points that shows the relationship between two sets of data; also called a scattergram.
Scientific notation
A way to write a number as a number from 1 up to (but not including) 10, multiplied by a power of ten.
Secant (of a circle)
A line that crosses a circle at exactly two points.
Sector
The part of a circle bounded by two radii and the arc between them, shaped like a slice of pie.
Segment
Part of a line with two endpoints; also called a line segment.
Semicircle
Half of a circle, cut off by a diameter. Its arc measures 180°.
Sequence
An ordered list of numbers, called terms, that often follow a rule.
Series
The sum of the terms of a sequence.
Set
A collection of distinct objects, called elements, usually listed inside braces.
Side
One of the line segments that make up a polygon, or one of the rays that form an angle.
Sieve of Eratosthenes
A method of finding prime numbers by listing numbers and crossing out the multiples of each prime in turn.
Sigma notation
A short way to write a sum using the Greek letter Σ, with the starting and ending values below and above it.
Significant figures
The digits in a number that carry meaning about its precision, starting from the first nonzero digit.
Similar figures
Figures with the same shape but not necessarily the same size. Their angles are equal and their sides are proportional.
Simple interest
Interest paid only on the original principal, found with I = Prt.
Simplest form
A fraction is in simplest form when its numerator and denominator have no common factor greater than 1.
Simplify
To rewrite an expression in its simplest form, for example by combining like terms or reducing a fraction.
Sine
In a right triangle, the ratio of the side opposite an angle to the hypotenuse: sin θ = opposite / hypotenuse.
Skew lines
Lines in space that are not in the same plane, so they never meet and are not parallel.
Skip counting
Counting forward by a number other than 1, such as by 2s, 5s or 10s.
Slant height
The distance from the apex of a pyramid or cone down the middle of a side face to the base edge.
Slope
A number that measures the steepness of a line: the rise divided by the run, m = (y₂ − y₁)/(x₂ − x₁).
Slope-intercept form
The equation of a line written as y = mx + b, where m is the slope and b is the y-intercept.
Solution
A value that makes an equation or inequality true.
Special right triangles
Right triangles with angles 45°-45°-90° or 30°-60°-90°, whose sides are in fixed ratios.
Speed
How fast something moves: the distance traveled divided by the time taken.
Sphere
A solid figure in which every point on the surface is the same distance from the center, like a ball or a globe.
Sprocket
A wheel with teeth that fit into the links of a chain, as on a bicycle. Its gear ratios use ratio and rate.
Square
A rectangle with four equal sides, or a rhombus with four right angles.
Square number
A number that is the product of a whole number and itself, such as 1, 4, 9 and 16.
Square root
A number that, multiplied by itself, gives the original number. The square root of 49 is 7.
Square unit
A square with sides 1 unit long, used to measure area, such as 1 cm² or 1 ft².
SSS congruence
Side-Side-Side: two triangles are congruent if all three pairs of sides are equal.
Standard deviation
A measure of how spread out data are from the mean. A small standard deviation means the data are close to the mean.
Standard form
A conventional way to write something: a number written with digits (3,405), a linear equation as Ax + By = C, or a polynomial with powers in decreasing order.
Stem-and-leaf plot
A display that splits each data value into a stem (leading digits) and a leaf (last digit) to show the distribution.
Straight angle
An angle that measures exactly 180°. Its two sides form a straight line.
Subset
A set whose elements all belong to another set. B is a subset of A, written B ⊆ A.
Substitution
Replacing a variable with a value or an equivalent expression. The substitution method solves a system by doing this.
Subtraction
Taking one amount away from another to find the difference, or finding how much greater one number is than another.
Subtrahend
The number being subtracted in a subtraction problem.
Sum
The result of adding two or more numbers.
Supplementary angles
Two angles whose measures add up to 180°.
Surface area
The total area of all the outer surfaces of a solid figure.
Survey
A way of collecting data by asking people questions.
Symmetry
A figure has symmetry when one part matches another after a reflection, rotation or other move. Line symmetry means it can be folded into matching halves.
System of equations
Two or more equations with the same variables, solved together. The solution makes all of them true; on a graph, it is where the lines cross.