Basic Math Definitions
We have collected some basic definitions on this page ... for lots more definitions, explanations, etc, use search:  
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Illustrated Mathematics Dictionary  

The Basic Operations
In basic mathematics there are many ways of saying the same thing:
Symbol 
Words Used 

+ 
Addition, Add, Sum, Plus, Increase, Total 
 
Subtraction, Subtract, Minus, Less, Difference, Decrease, Take Away, Deduct 
× 
Multiplication, Multiply, Product, By, Times, Lots Of 
÷ 
Division, Divide, Quotient, Goes Into, How Many Times 
Addition is ...
... bringing two or more numbers (or things) together to make a new total.
The numbers to be added together are called the "Addends": 
Subtraction is ...
... taking one number away from another.
Minuend  Subtrahend = Difference 

Minuend: The number that is to be subtracted from. 
Multiplication is ...
.. (in its simplest form) repeated addition.
Here we see that 6+6+6 (three 6s) make 18 It could also be said that 3+3+3+3+3+3 (six 3s) make 18 
But you can also multiply by fractions or decimals, which goes beyond the simple idea of repeated addition:
Example: 3.5 × 5 = 17.5
which is 3.5 lots of 5, or 5 lots of 3.5
Division is ...
... splitting into equal parts or groups. It is the result of "fair sharing".
Division has its own special words to remember.
Let's take the simple question of dividing 22 by 5. The answer is 4, with 2 left over. Here we illustrate the important words:
Which is the same as:
A Fraction is ...
.. part of a whole.
A number written with the bottom part (the denominator) telling you how many parts the whole is divided into, and the top part (the numerator) telling how many you have. 
See Fractions for more details.
A Decimal is ...
... a number based on 10. The numbers we use in everyday life are decimal numbers, because there are 10 digits (0,1,2,3,4,5,6,7,8 and 9).
it is also used to mean a number that uses a decimal point followed by digits as a way of showing values less than one. Example: 1.9 is a decimal number (one and nine tenths) 
See Decimals for more details.
A Percentage is ...
... parts per 100. The symbol is %
Example: 25% means 25 per 100 (25% of this box is green) 
See Percentages for more details.
Average
You calculate the average by adding up all the values, then divide by how many values.
Example: What is the average of 9, 2, 12 and 5?
Add up all the values: 9 + 2 + 12 + 5 = 28
Divide by how many values (there are four of them): 28 ÷ 4 = 7
So the average is 7
See Mean for more details.