A line that separates two places is a boundary line.
Radcliffe line separates India and Pakistan
There is one line, the equator, that separates the northern from the southern hemisphere.
The equator is an imaginary line that separates the Earth into the Northern Hemisphere and the Southern Hemisphere.
It is the solidus line that separates the numerator from the denominator in a fraction
A line of symmetry divides a figure into two matching halves.
It Separates BC (Line on top) into two congruent line segments.
A dividing line between two places is usually called a border.
The line that separates a shape into two matching halves is called the line of symmetry. When a shape is folded along this line, both halves mirror each other perfectly. In geometric figures, this line can be vertical, horizontal, or diagonal, depending on the shape's orientation.
A land bridge does not separate places. A land bridge connects them.
A divide.
That is usually known as the border.
Restate the question: What is the name for a line that crosses two parallel lines? Transversal