Glossary Entries
A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  ZData  Information collected and used to analyze a particular concept or situation.

Day  A unit used to measure time; 1 day = 24 hours.

Decagon  A decagon is a tensided shape (polygon).

Deciles  The 10th, 20th, 30th, ...90th percentile points (See definition for Percentile.) 
Decimal Fraction  A fraction using a decimal point to represent the denominator of 10 or a power of 10. 
Decimal Number  A fractional number that is written using base ten notation. A mixed decimal number has a whole number part as well. Example: 0.28 is a decimal number and 3.9 is a mixed decimal number.

Decimal Point  A period or dot separating the ones place from the tenths place in decimal numbers or dollars from cents in money. It looks like a period. Example: For "2.13" the decimal point is after the two. 
Decimeter  Onetenth of a meter, a decimeter is approximately the distance from one’s wrist to the end of one’s thumb.

Decompose  To break a number into smaller units to simplify computation. Example: 15 = 10 + 5.

Decomposition  The process of breaking a number into smaller units to simplify computation.

Decrease  To take away or become smaller.

Deductive Reasoning  Using logic to arrive at a conclusion from a given premise.

Degree  A unit used to measure angles. There are 360 degrees in a circle. 
Degree of a Monomial  The sum of the exponents on the variables contained in a term. Example: The degree of 3x^{3}y^{4} is 7. 
Degree of a Polynomial  The largest degree among all its terms. 
Denominator  The bottom number of a fraction. For 1/2 the denominator is 2. 
Density  The amount of mass per unit of volume. 
Dependent Events  Two events in which the outcome of the first event affects the outcome of the second event (e.g., drawing two marbles from a bag of red, green, and blue marbles without replacement). 
Diameter  The distance from one side of the circle to the other side when the line (chord) is drawn through the center point. It is a value that is two times the length of the radius. 
Difference  The answer in a subtraction problem. One value is subtracted form another and the result is the difference. Technically, the subtrahend is subtracted from the minuend. 
Digit  Any one of the ten numerical symbols:0, 1, 2, 3, 4, 5, 6, 7, 8, or 9. 
Digital Clock  A clock on which the time is displayed numerically. Example: The time is displayed as 12:22. It is twentytwo minutes after twelve o’clock. 
Dilation  A transformation that stretches or shrinks a function or graph both horizontally and vertically by the same scale factor. 
Dime  A coin with a value of 10 cents or one tenth of a dollar. 
Dimensional Analysis  A method of manipulating unit measures algebraically to determine the proper units for a quantity computed algebraically. For example, velocity has units of the form length over time (e.g., meters per second [ m/sec ]), and acceleration has units of velocity over time; so it follows that acceleration has units ( m/sec)/sec = m/(sec^{2}). 
Dimensions  Measurements of a figure. Examples include the length, width, and height of a prism. 
Direct Measurement  A process of obtaining the measurement of some entity by reading a measuring tool, such as a ruler for length, a scale for weight, or a protractor for angle size. 
Discount  A reduction made from the gross amount or value of something; a reduction made from the regular or list price. 
Discover  To make note of possible patterns and generalizations that result from investigation/exploration. 
Dispersion  The scattering of the values of a frequency distribution (of data) from an average. 
Distance  The length of the line segment joining two points. 
Distributive Property  A property of real numbers that states that the product of the sum or difference of two numbers is the same as the sum or difference of their products. Example: 6x(2+3)=(6x2)+(6x3)  Multiplication over addition. Example 2: 5 x 23 = 5 x (20 + 3) = 5 x 20 + 5 x 3 = 100 + 15 = 115. 
Dividend  A number that is divided by another number. 
Divisible  If a number has a whole number answer when divided by a second number, the first number is divisible by the second number; x is divisible by y if and only if x = qy where y is a whole number. 
Division  A mathematical operation involving two numbers that tells how many groups there are or how many are in each group. The symbol for division is ÷ or /. 
Divisor  The number by which the dividend is divided. 
Dollar  Currency that is worth 100 cents. You will see the symbol "$" when working with dollars. 
Domain  The set of values for which a function is defined. 
Double  To make twice as great or as many; to increase by adding an equal amount; to amount to twice the number. 
DoubleBar Graph  A graph that uses pairs of bars to compare and show the relationship between data. 
DoubleLine Graph  A graph that uses pairs of lines that show change over time to represent and compare data. 
Useful Reference Materials
Wikipedia:https://en.wikipedia.org/wiki/Fraction_%28mathematics%29
Encyclopædia Britannica:
http://www.britannica.com/topic/fraction
University of Delaware:
https://sites.google.com/a/udel.edu/fractions/