what do you call the line in a fraction
Fraction (mathematics) Informally, the numerator and denominator may be distinguished by placement alone but in formal contexts they are always separated by a fraction bar. The fraction bar may be horizontal (as in 1/3), oblique (as in 1/5), or diagonal (as in ​1⁄9).[3] These marks are respectively known as the horizontal bar, the slash (US) or stroke (UK), the division slash, and the fraction slash.[n 1] In typography, horizontal fractions are also known as "en" or "nut fractions" and diagonal fractions as "em fractions", based on the width of a line they take up.[3]