The procedure used in subtraction to "borrow" 10 from the next higher digit column in order to obtain a positive difference in the column in question.
Borrow
See also
CarryExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Borrow." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Borrow.html