Wow, super fast reply, thanks! I mean that you can say 'the sum of something' meaning the total amount of it. Also, 'sum of money' or 'lump sum' meaning the whole amount. It can also mean the result of an addition sum, as distinct from the sum itself (i.e. the numbers laid out on the page or the action of adding/subtracting/multiplying/whatever).
I've now said sum so many times that it sounds really weird in my head.
'sum' can mean the sum of parts and don't necessarily need to be numbers: "Summen av kreftene" = "The sum of the forces".
It can also mean the result of addition: "ledd + ledd = sum" = "term + term = sum"
I guess you could say 'den totale summen'(the total sum) instead if you wanted to be specific, but the distinction is often implied by context.