It is the solidus line that separates the numerator from the denominator in a fraction.
The line between the numerator and the denominator of a fraction is the the solidus line
It's called a vinculum.
This is the denominator, which is the bottom line of the fraction.
It's sometimes known as the 'divison bar' or 'fraction bar'.
The Vinculum, in some countries, is the name given to the horizontal line used to separate the numerator and denominator in a fraction.
The line separating the numerator and denominator when displayed as one number over another is called Vinculum, or sometimes referred to as the fraction bar. If the line is a slanting line (such as in "9/10"), it's referred to as the solidus.
Its called an Obelus I know it isn't an obelus its called Vinculum.