These words are often interchangeable. "Border" usually means a precise edging around something, like a border around a picture, or the border between places, like two countries. The "boundary" or "boundaries" of a country refers more to the entire body as a whole, not just the edges. The phrase "out of bonds," used in sports, means the ball was kicked/thrown/hit out of the designated area for playing, and the play becomes invalid. The ball crossed the border, leaving the boundaries. ("Boundaries" and "boundary" are often interchangeable too. Kind of weird but that's English for you! Also, "borderline" can be used, or "boundary line," in place of border unless you're talking about a squared/rectangular object, like a piece of paper that has decorations lining the edges - that's also a border, not so much a boundary). Boundary is also used to say when someone has done something ethically wrong, whether that's just your opinion, or a societal norm they disregarded. Let's say for example you're in a heated argument with a someone you work with. They are complaining about how you're doing your job, and they get so mad that they start insulting you, or even your friends/family. They've likely "crossed the boundary" of what is tolerable and what is not. As soon as they say or do something that you won't quickly forgive, they've crossed the ethical boundary you've set. I hope this helps! That was a good question, with a complicated answer, so let me know if you need me to simplify it more.

A border is a specific type of boundary.(border) for between countries or the edge of something. (boundary) it sounds like something you shouldn't cross.