Definition:Sum


 * Arithmetic:
 * Under the operation of addition of two numbers $a$ and $b$, the sum is the result of the operation $a + b$.


 * Algebra:
 * A summation is a repeated addition on a sequence (either finite or infinite) of numbers, usually signalled by the summation sign: $\ds \sum$


 * Abstract Algebra, Group Theory:
 * Definition:Direct Sum

Also see

 * Definition:Product
 * Definition:Difference