A vinculum is a horizontal line placed above multiple quantities to indicate that they form a unit. It is most commonly used to denote
1. A radical (
),
2. Repeating decimals (
),
3. The line segment 
joining two points 
and 
,
4. The complex conjugate 
,
5 Negation of a logical expression, 
,
6. A line placed over a Roman numerals character indicating that the overlined character value should be multiplied by a factor of 1000.
The term "viculum" may also be used to refer to the horizontal line used to separate the numerator from the denominator in a stacked (as opposed to in-line) fraction.
