https://www.youtube.com/watch?v=31zawn260B4

I admit I have never heard or used this expression in maths. I was taught that in additions you carry numbers, you borrow in subtractions and there is often a remainder in long divisions.

Starting in second grade, students begin to learn how to add and subtract numbers that are greater than one digit. To do this, they need to be taught how to regroup. This lesson will define regrouping and show examples for both addition and subtraction.
What Is Regrouping?
For some people, the thought of doing or teaching math is a traumatic experience. Hopefully, through this simple lesson, we will be able to help with that anxiety, at least when it comes to teaching regrouping.

In math, regrouping is the process of making groups of tens when adding or subtracting two digit numbers (or more) and is another name for carrying and borrowing . If that sounds like nonsense to you, fear not, because we will spell out the process clearly for you.

http://study.com/academy/lesson/what-is-regrouping-in-math-d...

Subtraction by "Regrouping"

(Also called "borrowing" or "trading")

To subtract numbers with more than one digit:

- write down the larger number first and the smaller number directly below it making sure to line up the columns!

- then do subtractions one column at a time like this (press play button):

https://www.mathsisfun.com/numbers/subtraction-regrouping.ht...

Sometimes your addition problems give you an answer that is greater than ten (10). For example, 6 + 6 = 12. When you start to add larger numbers, you will need to start "carrying" values. When we learned about addition, we used the term carry. Today, many math teachers use the term "regrouping". Carrying and regrouping are the same ideas.

http://www.numbernut.com/arithmetic/add-carry.html

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Note added at 48 mins (2016-12-15 16:44:54 GMT)
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How do I regroup in division?
Base-ten blocks can be used to show regrouping in division.
To model division problem, first show 174 with 1 hundred block, 7 tens blocks, and 4 ones blocks.

Base-ten blocks
Since the hundred block cannot be put into 3 equal groups without regrouping, regroup the hundred as 10 tens. Now there are 17 tens. Put an equal number of tens in each of the three groups.

https://www.eduplace.com/math/mw/background/4/05/te_4_05_div...