Prefix sum

Prefix Sum is like adding up numbers. We can add up the numbers in a list of numbers, one by one. For example, if we have a list of numbers like 3, 2, 5, 1, we can add up the numbers by starting with the first number (3) and then adding the second number to it (3 + 2 = 5). Then we add the third number to that (5 + 5 = 10) and keep doing this until we have added up all the numbers. We end up with the "Prefix Sum" which is the total of all the numbers in the list (3 + 2 + 5 + 1 = 11).