The common definition of a boundary is pretty straightforward. It is generally something that separates one thing from another.
For instance, it could be a fence separating your property from your neighbors. It might also be a median that divides parts of a highway.
There are natural boundaries too, like mountains or rivers that divide territories or nations. Basically, it is anything that is meant to keep something out or define where something that belongs to you (or someone else) begins and ends.Read more on everydaypower.com