Sum is the total you get when you add numbers together. When you add 5 + 3, the sum is 8. When you add up all the money in your piggy bank, you're finding the sum of your savings.

Teachers might ask you to “find the sum” of a set of numbers, which means add them all up. On a receipt, the sum at the bottom shows the total cost of everything you bought.

Beyond math, sum can describe a total amount of anything. The sum of your knowledge is everything you've learned. When someone talks about “the sum of their experiences,” they mean all their life experiences combined.

The phrase in sum means “to sum up” or “in total” and is used when wrapping up an explanation. After describing several problems with a plan, someone might say, “In sum, this won't work.”

There's also the verb form: when you sum up a book report, you briefly state its main points. And the adjective summary describes something that gives just the key points rather than every detail.