When you are adding numbers together to get a total, the numbers you are adding can be called addends or summands. The toatl is called the sum.
In the addition problem:
2 + 3 + 4 = 9
The numbers 2, 3, and 4 are called addends or summands. The number 9 is the sum.
All of the addends play the same roll--the contribute to the total. Addends can be added in any order, which is why all of those numbers get the same name:
2 + 3 + 4 = 4 + 3 + 2 = 4 + 2 + 3
When you subtracting one number from another, the numbers play different roles. One number is a total, largest amount that you are taking away from, that number is called the minuend. Another number is the amount taken away or deducted, that number is called the subtrahend. Find final amount that you get after taking away (or the space between the amounts if you are thinking of this in a compare context) is the difference.
In the subtraction problem:
12 - 8 = 4
The number 12 is the minuend, 8 is the subtrahend and 4 is the difference.
When you are subtracting, the order is important:
12 - 8 is not the same as 8 - 12
So, the numbers need different names. I didn't learn these names when I was a child, but they're awfully useful when I'm explaining things to you , so I need you to know what these words mean when I use them, and to be able to use them to explain things to me.