Definition of sum:
a quantity of money; "he borrowed a large sum"; "the amount he had in cash was insufficient"
a quantity obtained by the addition of a group of numbers
the final aggregate; "the sum of all our troubles did not equal the misery they suffered"
the choicest or most essential or most vital part of some idea or experience; "the gist of the prosecutor's argument"; "the heart and soul of the Republican Party"; "the nub of the story"
the whole amount
a set containing all and only the members of two or more given sets; "let C be the union of the sets A and B"
be a summary of; "The abstract summarizes the main ideas in the paper"
determine the sum of; "Add all the people in this town to those of the neighboring town"