The boundary separates worlds. It is a boundary.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
The place where that bridge is located is at the border between two countries.
Lately, I have the sense that my wife has established emotional boundaries between us.
My mom and I are always cautious of each other’s personal boundaries.