A vinculum is a horizontal line placed over a mathematical expression, used to indicate that it is to be considered a group.
Examples of its use include the case of a group of infinitely repeating digits, for example,
It is also used in the notation of a radical to indicate the radicand whose root is being indicated. In the case of
![\sqrt[n]{ab+2}](a/../upload/math/8080f31cf28dcb85bfe46f8386cd7202.png)
the quantity ab + 2 is the radicand, and thus has a vinculum over it.
The vinculum is also sometimes used in Boolean algebra, where it serves to indicate a group of expressions whose logical result is to be NOTed, as in
