Specifically, the horizontal line between the numerator and denominator in a fraction
{i} tie, bond; line appearing above two terms showing that they should be considered as one entity (Mathematics); ligaments which limit the movement of an organ (Anatomy)
A horizontal line used to separate the numerator from the denominator in a fraction, or over the top of part of a calculation and serving the same purpose as parentheses (ie, indicating that this part of the calculation is to be done before other parts)
A straight, horizontal mark placed over two or more members of a compound quantity, which are to be subjected to the same operation, as in the expression x2 + y2 - x + y