A line that separates two places is a boundary line.
border
Radcliffe line separates India and Pakistan
There is one line, the equator, that separates the northern from the southern hemisphere.
It is the solidus line that separates the numerator from the denominator in a fraction
It Separates BC (Line on top) into two congruent line segments.
A line of symmetry divides a figure into two matching halves.
The Equator or Prime Meridian
A land bridge does not separate places. A land bridge connects them.
A dividing line between two places is usually called a border.
A divide.
That is usually known as the border.
The line that separates the day and night is called the "TERMINATOR". it is a grey moving line
Restate the question: What is the name for a line that crosses two parallel lines? Transversal