The ~ of an area of land is an imaginary line that separates it from other areas.
...the Bow Brook which forms the western ~ of the wood...
Drug traffickers operate across national boundaries.
= border, frontier
N-COUNT: oft N of/between n
The boundaries of something such as a subject or activity are the limits that people think that it has.
The boundaries between history and storytelling are always being blurred and muddled.
...extending the boundaries of press freedom.
N-COUNT: usu pl, oft N of/between n