I should mention that some of these definitions are unique to US English. The meanings may vary in other English-speaking countries around the world. Math symbols also vary - for example, the function of the decimal "point" (as we call it) is performed by a "comma" in other countries. For a fun diversion you could visit Jenny Eather's Maths Dictionary for Kids (she is based in Australia)

You are welcome to download an illustrated, expanded version of this glossary in English or Spanish from the Excel Math website.

Our next group begins with the letters D through K

**Day**unit of time containing 24 hours; equal to one rotation of the Earth**Decimal**(1) symbol used to separate whole numbers from smaller parts of a whole**Decimal**(2) symbol used to separate dollar amounts from cents**Decimal**(3) word that refers to 10**Decimal**(4) math system based on 10 different digits**Decimal Number**number with a decimal point; not a whole number**Deductive Reasoning**logical process; begins with evidence and draws a conclusion; used to solve word problems**Denominator**portion of a fraction written below the line; the total number of parts into which a whole number is divided**Density**(1) ratio of the weight or mass of a material to its volume**Density**(2) the number of individual items in a given space or region**Diagonal**line segment completely inside a polygon that connects two of its non-adjoining vertices**Diameter**line segment passing through the center of a circle, ending at either side of the circle**Distributive Property: Multiplication**multiplying the sum of several addends gives the same result as individually multiplying the addends first, then adding the products (A + B) x C = (A x C) + (B x C)**Dividend**quantity to be divided; beginning number from which repeated subtractions are taken**Divisor**quantity by which a dividend is divided; amount repeatedly subtracted from a dividend

**Edge**line segment where 2 faces on a 3D figure meet; flat or curved**Empty Set**a set that contains no items; not the same as a set containing a zero**Equally Likely**multiple events with the same probability of occurring; probability value of 0.5**Equation**number statement that includes an equal symbol =**Equilateral Triangle**plane or 2D figure whose 3 sides are equal in length**Equivalent Fractions**fractions with the same value expressed using different numbers; 4/8 is equivalent to 2/4 and 1/2**Estimate**to quickly calculate a number that is tolerably close to the exact answer**Even Number**number that can be divided into two equal groups; all even numbers end in 0, 2, 4, 6 or 8**Exterior Angle**an angle on the outside of 2 parallel lines that are intersected by another line

**Face**2D polygon (plane figure) that forms one side of a 3D figure**Fact Family**related addition/subtraction or multiplication/division facts involving the same set of numbers**Factor**number that divides evenly into another number.**Factorial**product generated by multiplying a number and every positive number less than the number**Fahrenheit (F)**temperature scale with 180 units between the freezing point (32) and the boiling point (212) of water**Flip**change in location of a figure that results in a mirror image of the original figure; Reflection**Formula**a mathematical statement or rule used in calculations

**Greater Than**number of higher, or larger, value than another number; symbol >**Greatest Common Factor**the largest factor of two or more numbers**Greatest to Least**arrangement of numbers from highest value to lowest value

**Height**vertical dimension of a 2D or 3D figure**Hexagon**polygon with exactly six sides**Histogram**graph where the labels for the bars are numerical intervals; used to compare data

**Impossible Event**event that will not happen; probability value of 0.0**Improper Fraction**fraction where the numerator is greater than or equal to the denominator**Inequality**number statement that compares two unequal expressions**Integer**a whole number and its opposite (-2,-1,0,1,2)**Intercept**point where a line or curve meets the x- or y-axis on a grid**Interest 1)**fee charged by a lender to a borrower for use of money**Interest 2)**fee a bank pays to its depositors; often a percentage of the deposit, calculated over a period of time (5% per month)**Interior Angle**angle on the inside of two parallel lines that are intersected by another line**Intersecting Lines**lines that cross at some point**Intersection of Sets**a group of values or items that are common to all the sets being evaluated**Isosceles Triangle**triangle having only 2 sides of equal length