a fraction bar By Hoggyilove animals: A vinculum is what it's called
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 that separates the top number (numerator) from the bottom number (denominator) of a fraction can be called a dividing line - since this is what is happening in the sum itself to calculate the fraction.
If it's a fraction then it's the denominator which divides into the numerator
An imaginary line that divides a mirror in half is called a plane.
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.
the halfcourt line
The imaginary line that divides the earth into the northern and southern hemispheres is called Equator, the line that divides it into the eastern and western hemispheres is the prime meridian.