A vinculum is a mathematical symbol used to indicate a grouping of terms or numbers. It is often represented as a horizontal line that connects elements, such as in fractions or radicals. For example, in the fraction a/b, the vinculum appears above the denominator, showing that a is divided by b. In addition to its use in fractions, the vinculum can also denote repeating decimals. For instance, in the decimal 0.333..., a vinculum placed over the 3 indicates that the 3 repeats indefinitely. This helps clarify the structure of numbers in mathematical expressions.