en.wikipedia.org/wiki/Summation

In mathematics, summation (capital Greek sigma symbol: ∑) is the addition of a
sequence of numbers; the result is their **sum** or total. If numbers are added
sequentially from left to right, any intermediate result is a partial **sum**, prefix **sum**,
or running total of the summation. The numbers to be summed (called addends, ...

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**Math** explained in easy language, plus puzzles, games, quizzes, worksheets and
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www.dictionary.com/browse/sum

**Sum** definition, the aggregate of two or more numbers, magnitudes, quantities, or
particulars as determined by or as if by the **mathematical** process of addition: The
**sum** of 6 and 8 is 14. See more.

www.dr-aart.nl/Arithmetic-sum-difference-product-quotient.html

**Sum**. The **sum** of two or more numbers is the outcome of adding these numbers.
Example: Calculate the **sum** of 13, 5 and 8. Answer: 13 + 5 + 8 = 26. The parts
you add are called terms. Example: Which terms are in the formula y = 3 x ^{2} + 6 x
+ 8? Answer: Three terms, namely 3 x ^{2}, 6 x and 8.

www.mathsteacher.com.au/year8/ch01_arithmetic/01_basic/oper.htm

Recall: The four basic **mathematical** operations are: Addition, subtraction,
multiplication and division. Addition. Adding two (or more) numbers means to find
their **sum** (or total). The symbol used for addition is '+'. For example, 5 + 10 = 15.
This is read as five plus ten is equal to fifteen or simply, five plus ten is fifteen.
Example ...

www.khanacademy.org/math/algebra2/sequences-and-series/alg2-sigma-notation/v/sigma-notation-sum

What I want to do in this video is introduce you to the idea of Sigma notation,
which will be used extensively through your **mathematical** career. So let's just say
you wanted to find a **sum** of some terms, and these terms have a pattern. So let's
say you want to find the **sum** of the first 10 numbers. So you could say 1 plus 2
plus ...

mathworld.wolfram.com/Sum.html

The numbers being summed are called addends, or sometimes summands. The
summation operation can also be indicated using a capital sigma with upper and
lower limits written above and below, and the index indicated below. For example
, the above **sum** could be written ...

www.splashmath.com/math-vocabulary/addition/sum

Definition of **Sum** explained with illustrated examples. Also, practice lots of **math**
problems with fun **math** worksheets at Splash **Math**.