( dividing lines)
1.
A dividing line is a distinction or set of distinctions which marks the difference between two types of thing or two groups.
There’s a very thin dividing line between joviality and hysteria.
N-COUNT : usu sing , oft N between pl-n
2.
The dividing line between two areas is the boundary between them.
...people on both sides of the dividing line between Israel and the occupied territories.
N-SING : oft N between pl-n