The line or area separating geopolitical units
They remain at the boundary of his kingdom and Corcoran.
The Nerbudda river formed the boundary between the two empires.
Drago], the deep ravine of which forms the western boundary and defence of the city.
I prefer not to cross state lines with my prizes, but Delaware is such a small state I'd left its boundary before I realized.
As in, when I say the word boundary, you stop whatever it is you're doing or about to do and leave me alone.